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<HTML><HEAD><TITLE>BASH(1) Manual Page</TITLE></HEAD><BODY><TABLE WIDTH=100%><TR><TH ALIGN=LEFT width=33%>BASH(1)<TH ALIGN=CENTER width=33%>2022 September 19<TH ALIGN=RIGHT width=33%>BASH(1)</TR></TABLE><BR><A HREF="#index">Index</A><HR>                               <A NAME="lbAB">&nbsp;</A><H3>NAME</H3> bash - GNU Bourne-Again SHell<A NAME="lbAC">&nbsp;</A><H3>SYNOPSIS</H3> <B>bash</B> [options][command_string | file]<A NAME="lbAD">&nbsp;</A><H3>COPYRIGHT</H3>  Bash is Copyright &#169; 1989-2022 by the Free Software Foundation, Inc.<A NAME="lbAE">&nbsp;</A><H3>DESCRIPTION</H3> <B>Bash</B> is an <B>sh</B>-compatible command language interpreter thatexecutes commands read from the standard input or from a file.<B>Bash</B> also incorporates useful features from the <I>Korn</I> and <I>C</I>shells (<B>ksh</B> and <B>csh</B>).<P> <B>Bash</B> is intended to be a conformant implementation of theShell and Utilities portion of the IEEE POSIX specification(IEEE Standard 1003.1).<B>Bash</B> can be configured to be POSIX-conformant by default.<A NAME="lbAF">&nbsp;</A><H3>OPTIONS</H3> All of the single-character shell options documented in thedescription of the <B>set</B> builtin command, including <B>-o</B>,can be used as options when the shell is invoked.In addition, <B>bash</B>interprets the following options when it is invoked:<P>  <DL COMPACT><DT><B>-c</B> <DD>If the<B>-c</B> option is present, then commands are read from the first non-option argument<I>command_string</I>. If there are arguments after the<I>command_string</I>, the first argument is assigned to<B>$0</B> and any remaining arguments are assigned to the positional parameters.The assignment to<B>$0</B> sets the name of the shell, which is used in warning and error messages.<DT><B>-i</B> <DD>If the<B>-i</B> option is present, the shell is<I>interactive</I>. <DT><B>-l</B> <DD>Make<B>bash</B> act as if it had been invoked as a login shell (see<FONT SIZE=-1><B>INVOCATION</B> </FONT>below).<DT><B>-r</B> <DD>If the<B>-r</B> option is present, the shell becomes<I>restricted</I> (see<FONT SIZE=-1><B>RESTRICTED SHELL</B> </FONT>below).<DT><B>-s</B> <DD>If the<B>-s</B> option is present, or if no arguments remain after optionprocessing, then commands are read from the standard input.This option allows the positional parameters to be setwhen invoking an interactive shell or when reading inputthrough a pipe.<DT><B>-D</B> <DD>A list of all double-quoted strings preceded by <B>$</B>is printed on the standard output.These are the strings thatare subject to language translation when the current localeis not <B>C</B> or <B>POSIX</B>.This implies the <B>-n</B> option; no commands will be executed.<DT><B>[-+]O [</B><I>shopt_option</I>] <DD><I>shopt_option</I> is one of the shell options accepted by the<B>shopt</B> builtin (see<FONT SIZE=-1><B>SHELL BUILTIN COMMANDS</B> </FONT>below).If <I>shopt_option</I> is present, <B>-O</B> sets the value of that option;<B>+O</B> unsets it.If <I>shopt_option</I> is not supplied, the names and values of the shelloptions accepted by <B>shopt</B> are printed on the standard output.If the invocation option is <B>+O</B>, the output is displayed in a formatthat may be reused as input.<DT><B>--</B> <DD>A<B>--</B> signals the end of options and disables further option processing.Any arguments after the<B>--</B> are treated as filenames and arguments.  An argument of<B>-</B> is equivalent to <B>--</B>. </DL><P> <B>Bash</B> also interprets a number of multi-character options.These options must appear on the command line before thesingle-character options to be recognized.<P>  <DL COMPACT><DT><B>--debugger</B> <DD>Arrange for the debugger profile to be executed before the shellstarts.Turns on extended debugging mode (see the description of the<B>extdebug</B> option to the<B>shopt</B> builtin below).<DT><B>--dump-po-strings</B> <DD>Equivalent to <B>-D</B>, but the output is in the GNU <I>gettext</I><B>po</B> (portable object) file format.<DT><B>--dump-strings</B> <DD>Equivalent to <B>-D</B>.<DT><B>--help</B> <DD>Display a usage message on standard output and exit successfully.<DT><B>--init-file</B> <I>file</I><DD> <DT><B>--rcfile</B> <I>file</I><DD> Execute commands from<I>file</I> instead of the standard personal initialization file<A HREF="file:~/.bashrc"><I>~/.bashrc</I></A> if the shell is interactive (see<FONT SIZE=-1><B>INVOCATION</B> </FONT>below).<DT><B>--login</B> <DD>Equivalent to <B>-l</B>.<DT><B>--noediting</B> <DD>Do not use the GNU<B>readline</B> library to read command lines when the shell is interactive.<DT><B>--noprofile</B> <DD>Do not read either the system-wide startup file <A HREF="file:/etc/profile"><I>/etc/profile</I></A> or any of the personal initialization files<A HREF="file:~/.bash_profile"><I>~/.bash_profile</I></A>, <A HREF="file:~/.bash_login"><I>~/.bash_login</I></A>, or<A HREF="file:~/.profile"><I>~/.profile</I></A>. By default,<B>bash</B> reads these files when it is invoked as a login shell (see<FONT SIZE=-1><B>INVOCATION</B> </FONT>below).<DT><B>--norc</B> <DD>Do not read and execute the personal initialization file<A HREF="file:~/.bashrc"><I>~/.bashrc</I></A> if the shell is interactive.This option is on by default if the shell is invoked as<B>sh</B>. <DT><B>--posix</B> <DD>Change the behavior of <B>bash</B> where the default operation differsfrom the POSIX standard to match the standard (<I>posix mode</I>).See<FONT SIZE=-1><B>SEE ALSO</B> </FONT>below for a reference to a document that details how posix mode affectsbash's behavior.<DT><B>--restricted</B> <DD>The shell becomes restricted (see<FONT SIZE=-1><B>RESTRICTED SHELL</B> </FONT>below).<DT><B>--verbose</B> <DD>Equivalent to <B>-v</B>.<DT><B>--version</B> <DD>Show version information for this instance of<B>bash</B> on the standard output and exit successfully. </DL><A NAME="lbAG">&nbsp;</A><H3>ARGUMENTS</H3> If arguments remain after option processing, and neither the<B>-c</B> nor the<B>-s</B> option has been supplied, the first argument is assumed tobe the name of a file containing shell commands.If<B>bash</B> is invoked in this fashion,<B>$0</B> is set to the name of the file, and the positional parametersare set to the remaining arguments.<B>Bash</B> reads and executes commands from this file, then exits.<B>Bash</B>'s exit status is the exit status of the last commandexecuted in the script.If no commands are executed, the exit status is 0.An attempt is first made to open the file in the current directory, and,if no file is found, then the shell searches the directories in<FONT SIZE=-1><B>PATH</B> </FONT>for the script.<A NAME="lbAH">&nbsp;</A><H3>INVOCATION</H3> A <I>login shell</I> is one whose first character of argument zero is a<B>-</B>, or one started with the<B>--login</B> option.<P> An <I>interactive</I> shell is one started without non-option arguments(unless <B>-s</B> is specified)and without the<B>-c</B> option,whose standard input and error areboth connected to terminals (as determined by<I>isatty</I>(3)), or one started with the<B>-i</B> option.<FONT SIZE=-1><B>PS1</B> </FONT>is set and<B>$-</B> includes<B>i</B> if<B>bash</B> is interactive,allowing a shell script or a startup file to test this state.<P> The following paragraphs describe how<B>bash</B> executes its startup files.If any of the files exist but cannot be read,<B>bash</B> reports an error.Tildes are expanded in filenames as described below under<B>Tilde Expansion</B> in the<FONT SIZE=-1><B>EXPANSION</B> </FONT>section.<P> When<B>bash</B> is invoked as an interactive login shell, or as a non-interactive shellwith the <B>--login</B> option, it first reads andexecutes commands from the file <A HREF="file:/etc/profile"><I>/etc/profile</I></A>, if thatfile exists.After reading that file, it looks for <A HREF="file:~/.bash_profile"><I>~/.bash_profile</I></A>,<A HREF="file:~/.bash_login"><I>~/.bash_login</I></A>, and <A HREF="file:~/.profile"><I>~/.profile</I></A>, in that order, and readsand executes commands from the first one that exists and is readable.The<B>--noprofile</B> option may be used when the shell is started to inhibit this behavior.<P> When an interactive login shell exits,or a non-interactive login shell executes the <B>exit</B> builtin command,<B>bash</B> reads and executes commands from the file <A HREF="file:~/.bash_logout"><I>~/.bash_logout</I></A>, if itexists.<P> When an interactive shell that is not a login shell is started,<B>bash</B> reads and executes commands from <A HREF="file:~/.bashrc"><I>~/.bashrc</I></A>, if that file exists.This may be inhibited by using the<B>--norc</B> option.The <B>--rcfile</B> <I>file</I> option will force<B>bash</B> to read and execute commands from <I>file</I> instead of <A HREF="file:~/.bashrc"><I>~/.bashrc</I></A>.<P> When<B>bash</B> is started non-interactively, to run a shell script, for example, itlooks for the variable<FONT SIZE=-1><B>BASH_ENV</B> </FONT>in the environment, expands its value if it appears there, and uses theexpanded value as the name of a file to read and execute.<B>Bash</B> behaves as if the following command were executed:<P><DL COMPACT><DT><DD><TT>if [ -n &quot;$BASH_ENV&quot; ]; then . &quot;$BASH_ENV&quot;; fi</TT> </DL> <P>but the value of the<FONT SIZE=-1><B>PATH</B> </FONT>variable is not used to search for the filename.<P> If<B>bash</B> is invoked with the name<B>sh</B>, it tries to mimic the startup behavior of historical versions of<B>sh</B> as closely as possible,while conforming to the POSIX standard as well.When invoked as an interactive login shell, or a non-interactiveshell with the <B>--login</B> option, it first attempts toread and execute commands from<A HREF="file:/etc/profile"><I>/etc/profile</I></A> and<A HREF="file:~/.profile"><I>~/.profile</I></A>, in that order.The<B>--noprofile</B> option may be used to inhibit this behavior.When invoked as an interactive shell with the name<B>sh</B>, <B>bash</B> looks for the variable<FONT SIZE=-1><B>ENV</B>, </FONT>expands its value if it is defined, and uses theexpanded value as the name of a file to read and execute.Since a shell invoked as<B>sh</B> does not attempt to read and execute commands from any other startupfiles, the<B>--rcfile</B> option has no effect.A non-interactive shell invoked with the name<B>sh</B> does not attempt to read any other startup files.When invoked as<B>sh</B>, <B>bash</B> enters<I>posix</I> mode after the startup files are read.<P> When<B>bash</B> is started in<I>posix</I> mode, as with the<B>--posix</B> command line option, it follows the POSIX standard for startup files.In this mode, interactive shells expand the<FONT SIZE=-1><B>ENV</B> </FONT>variable and commands are read and executed from the filewhose name is the expanded value.No other startup files are read.<P> <B>Bash</B> attempts to determine when it is being run with its standard inputconnected to a network connection, as when executed bythe historical remote shell daemon, usually <I>rshd</I>,or the secure shell daemon <I>sshd</I>.If<B>bash</B> determines it is being run non-interactively in this fashion,it reads and executes commands from <A HREF="file:~/.bashrc"><I>~/.bashrc</I></A>,if that file exists and is readable.It will not do this if invoked as <B>sh</B>.The<B>--norc</B> option may be used to inhibit this behavior, and the<B>--rcfile</B> option may be used to force another file to be read, but neither<I>rshd</I> nor <I>sshd</I> generally invoke the shell with those optionsor allow them to be specified.<P> If the shell is started with the effective user (group) id not equal to thereal user (group) id, and the <B>-p</B> option is not supplied, no startupfiles are read, shell functions are not inherited from the environment, the<FONT SIZE=-1><B>SHELLOPTS</B>, </FONT><FONT SIZE=-1><B>BASHOPTS</B>, </FONT><FONT SIZE=-1><B>CDPATH</B>, </FONT>and<FONT SIZE=-1><B>GLOBIGNORE</B> </FONT>variables, if they appear in the environment, are ignored,and the effective user id is set to the real user id.If the <B>-p</B> option is supplied at invocation, the startup behavior isthe same, but the effective user id is not reset.<A NAME="lbAI">&nbsp;</A><H3>DEFINITIONS</H3> The following definitions are used throughout the rest of thisdocument. <DL COMPACT><DT><B>blank</B> <DD>A space or tab.<DT><B>word</B> <DD>A sequence of characters considered as a single unit by the shell.Also known as a<B>token</B>. <DT><B>name</B> <DD>A<I>word</I> consisting only of alphanumeric characters and underscores, andbeginning with an alphabetic character or an underscore.  Alsoreferred to as an<B>identifier</B>. <DT><B>metacharacter</B> <DD>A character that, when unquoted, separates words.  One of the following:<BR> <DL COMPACT><DT><DD><P> <B>|  &amp;  ;  (  )  &lt;  &gt;  space  tab  newline</B> </DL> <DT><B>control operator</B> <DD>A <I>token</I> that performs a control function.  It is one of the followingsymbols:<DL COMPACT><DT><DD><P> <B>||  &amp;  &amp;&amp;  ;  ;;  ;&amp;  ;;&amp;  (  )  |  |&amp;    &lt;newline&gt;</B> </DL>  </DL><A NAME="lbAJ">&nbsp;</A><H3>RESERVED WORDS</H3> <I>Reserved words</I> are words that have a special meaning to the shell.The following words are recognized as reserved when unquoted and eitherthe first word of a command (see<FONT SIZE=-1><B>SHELL GRAMMAR</B> </FONT>below), the third word of a<B>case</B> or<B>select</B> command(only <B>in</B> is valid), or the third word of a<B>for</B> command (only <B>in</B> and <B>do</B> are valid):<DL COMPACT><DT><DD> <P> <B></B> !    case    coproc    do    done    elif    else    esac    fi    for    function    if    in    select    then    until    while    {    }    time    [[    ]]</DL>  <A NAME="lbAK">&nbsp;</A><H3>SHELL GRAMMAR</H3> This section describes the syntax of the various forms of shell commands.<A NAME="lbAL">&nbsp;</A><H4>Simple Commands</H4> A <I>simple command</I> is a sequence of optional variable assignmentsfollowed by <B>blank</B>-separated words and redirections, andterminated by a <I>control operator</I>.  The first wordspecifies the command to be executed, and is passed as argument zero.The remaining words are passed as arguments to the invoked command.<P> The return value of a <I>simple command</I> is its exit status, or128+<I>n</I> if the command is terminated by signal<I>n</I>. <A NAME="lbAM">&nbsp;</A><H4>Pipelines</H4> A <I>pipeline</I> is a sequence of one or more commands separated byone of the control operators<B>|</B> or <B>|&amp;</B>.The format for a pipeline is:<DL COMPACT><DT><DD><P> [<B>time</B> [<B>-p</B>]] [ ! ] <I>command1</I> [ [<B>|</B>|<B>|&amp;</B>] <I>command2</I> ... ]</DL> <P> The standard output of<I>command1</I> is connected via a pipe to the standard input of<I>command2</I>. This connection is performed before any redirections specified by the<I>command1</I>(see <FONT SIZE=-1><B>REDIRECTION</B> </FONT>below).If <B>|&amp;</B> is used, <I>command1</I>'s standard error, in addition to itsstandard output, is connected to<I>command2</I>'s standard input through the pipe;it is shorthand for <B>2&gt;&amp;1 |</B>.This implicit redirection of the standard error to the standard output isperformed after any redirections specified by <I>command1</I>.<P> The return status of a pipeline is the exit status of the lastcommand, unless the <B>pipefail</B> option is enabled.If <B>pipefail</B> is enabled, the pipeline's return status is thevalue of the last (rightmost) command to exit with a non-zero status,or zero if all commands exit successfully.If the reserved word<B>!</B> precedes a pipeline, the exit status of that pipeline is the logicalnegation of the exit status as described above.The shell waits for all commands in the pipeline toterminate before returning a value.<P> If the<B>time</B> reserved word precedes a pipeline, the elapsed as well as user andsystem time consumed by its execution are reported when the pipelineterminates.The <B>-p</B> option changes the output format to that specified by POSIX.When the shell is in <I>posix mode</I>, it does not recognize<B>time</B> as a reserved word if the next token begins with a `-'.The<FONT SIZE=-1><B>TIMEFORMAT</B> </FONT>variable may be set to a format string that specifies how the timinginformation should be displayed; see the description of<FONT SIZE=-1><B>TIMEFORMAT</B> </FONT>under<B>Shell Variables</B> below.<P> When the shell is in <I>posix mode</I>, <B>time</B>may be followed by a newline.  In this case, the shell displays thetotal user and system time consumed by the shell and its children.The<FONT SIZE=-1><B>TIMEFORMAT</B> </FONT>variable may be used to specify the format ofthe time information.<P> Each command in a multi-command pipeline,where pipes are created,is executed in a <I>subshell</I>, which is aseparate process.See<FONT SIZE=-1><B>COMMAND EXECUTION ENVIRONMENT</B></FONT>for a description of subshells and a subshell environment.If the <B>lastpipe</B> option is enabled using the <B>shopt</B> builtin(see the description of <B>shopt</B> below),the last element of a pipeline may be run by the shell processwhen job control is not active.<A NAME="lbAN">&nbsp;</A><H4>Lists</H4> A <I>list</I> is a sequence of one or more pipelines separated by oneof the operators<B>;</B>, <B>&amp;</B>, <B>&amp;&amp;</B>, or<B>||</B>, and optionally terminated by one of<B>;</B>, <B>&amp;</B>, or<B>&lt;newline&gt;</B>. <P> Of these list operators,<B>&amp;&amp;</B> and<B>||</B> have equal precedence, followed by<B>;</B> and<B>&amp;</B>, which have equal precedence.<P> A sequence of one or more newlines may appear in a <I>list</I> insteadof a semicolon to delimit commands.<P> If a command is terminated by the control operator<B>&amp;</B>, the shell executes the command in the <I>background</I>in a subshell.The shell does not wait for the command tofinish, and the return status is 0.These are referred to as <I>asynchronous</I> commands.Commands separated by a<B>;</B> are executed sequentially; the shell waits for eachcommand to terminate in turn.  The return status is theexit status of the last command executed.<P> AND and OR lists are sequences of one or more pipelines separated by the<B>&amp;&amp;</B> and <B>||</B> control operators, respectively.AND and OR lists are executed with left associativity.An AND list has the form<DL COMPACT><DT><DD><P> <I>command1</I> <B>&amp;&amp;</B> <I>command2</I></DL> <P> <I>command2</I> is executed if, and only if,<I>command1</I> returns an exit status of zero (success).<P> An OR list has the form<DL COMPACT><DT><DD><P> <I>command1</I> <B>||</B> <I>command2</I></DL> <P> <I>command2</I> is executed if, and only if,<I>command1</I> returns a non-zero exit status.The return status ofAND and OR lists is the exit status of the last commandexecuted in the list.<A NAME="lbAO">&nbsp;</A><H4>Compound Commands</H4> A <I>compound command</I> is one of the following.In most cases a <I>list</I> in a command's description may be separated fromthe rest of the command by one or more newlines, and may be followed by anewline in place of a semicolon.<DL COMPACT><DT>(<I>list</I>)<DD><I>list</I> is executed in a subshell (see<FONT SIZE=-1><B>COMMAND EXECUTION ENVIRONMENT</B></FONT>below for a description of a subshell environment).Variable assignments and builtincommands that affect the shell's environment do not remain in effectafter the command completes.  The return status is the exit status of<I>list</I>.<DT>{ <I>list</I>; }<DD><I>list</I> is simply executed in the current shell environment.<I>list</I> must be terminated with a newline or semicolon.This is known as a <I>group command</I>.The return status is the exit status of<I>list</I>.Note that unlike the metacharacters <B>(</B> and <B>)</B>, <B>{</B> and<B>}</B> are <I>reserved words</I> and must occur where a reservedword is permitted to be recognized.  Since they do not cause a wordbreak, they must be separated from <I>list</I> by whitespace or anothershell metacharacter.<DT>((<I>expression</I>))<DD>The <I>expression</I> is evaluated according to the rules describedbelow under<FONT SIZE=-1><B>ARITHMETIC EVALUATION</B>. </FONT>If the value of the expression is non-zero, the return status is 0;otherwise the return status is 1.The <I>expression</I>undergoes the same expansionsas if it were within double quotes,but double quote characters in <I>expression</I> are not treated speciallyand are removed.<DT><B>[[</B> <I>expression</I> <B>]]</B><DD>Return a status of 0 or 1 depending on the evaluation ofthe conditional expression <I>expression</I>.Expressions are composed of the primaries described below under<FONT SIZE=-1><B>CONDITIONAL EXPRESSIONS</B>. </FONT>The words between the <B>[[</B> and <B>]]</B> do not undergo word splittingand pathname expansion.The shell performs tilde expansion, parameter andvariable expansion, arithmetic expansion, command substitution, processsubstitution, and quote removal on those words(the expansions that would occur if the words were enclosed in double quotes).Conditional operators such as <B>-f</B> must be unquoted to be recognizedas primaries.<P>  When used with <B>[[</B>, the <B>&lt;</B> and <B>&gt;</B> operators sortlexicographically using the current locale.<P>  When the <B>==</B> and <B>!=</B> operators are used, the string to theright of the operator is considered a pattern and matched accordingto the rules described below under <B>Pattern Matching</B>,as if the <B>extglob</B> shell option were enabled.The <B>=</B> operator is equivalent to <B>==</B>.If the<B>nocasematch</B> shell option is enabled, the match is performed without regard to the caseof alphabetic characters.The return value is 0 if the string matches (<B>==</B>) or does not match(<B>!=</B>) the pattern, and 1 otherwise.Any part of the pattern may be quoted to force the quoted portionto be matched as a string.<P>  An additional binary operator, <B>=~</B>, is available, with the sameprecedence as <B>==</B> and <B>!=</B>.When it is used, the string to the right of the operator is considereda POSIX extended regular expression and matched accordingly(using the POSIX <I>regcomp</I> and <I>regexec</I> interfacesusually described in <I>regex</I>(3)).The return value is 0 if the string matchesthe pattern, and 1 otherwise.If the regular expression is syntactically incorrect, the conditionalexpression's return value is 2.If the<B>nocasematch</B> shell option is enabled, the match is performed without regard to the caseof alphabetic characters.If any part of the pattern is quoted, the quoted portion is matched literally.This means every character in the quoted portion matches itself,instead of having any special pattern matching meaning.If the pattern is stored in a shell variable, quoting the variableexpansion forces the entire pattern to be matched literally.Treat bracket expressions in regular expressions carefully,since normal quoting and pattern characters lose their meaningsbetween brackets.<P>  The pattern will match if it matches any part of the string.Anchor the pattern using the <B>^</B> and <B>$</B> regular expressionoperators to force it to match the entire string.The array variable<FONT SIZE=-1><B>BASH_REMATCH</B> </FONT>records which parts of the string matched the pattern.The element of<FONT SIZE=-1><B>BASH_REMATCH</B> </FONT>with index 0 contains the portion ofthe string matching the entire regular expression.Substrings matched by parenthesized subexpressions within the regularexpression are saved in the remaining<FONT SIZE=-1><B>BASH_REMATCH</B> </FONT>indices. The element of<FONT SIZE=-1><B>BASH_REMATCH</B> </FONT>with index <I>n</I> is the portion of thestring matching the <I>n</I>th parenthesized subexpression.Bash sets<FONT SIZE=-1><B>BASH_REMATCH</B> </FONT>in the global scope; declaring it as a local variable will lead tounexpected results.<P>  Expressions may be combined using the following operators, listedin decreasing order of precedence:<P>  <DL COMPACT><DT><DD> <DL COMPACT><DT><B>( </B><I>expression</I> ) <DD>Returns the value of <I>expression</I>.This may be used to override the normal precedence of operators.<DT><B>! </B><I>expression</I> <DD>True if<I>expression</I> is false.<DT><I>expression1</I> <B>&amp;&amp;</B> <I>expression2</I><DD>True if both<I>expression1</I> and<I>expression2</I> are true.<DT><I>expression1</I> <B>||</B> <I>expression2</I><DD>True if either<I>expression1</I> or<I>expression2</I> is true. </DL><P> The <B>&amp;&amp;</B> and <B>||</B>operators do not evaluate <I>expression2</I> if the value of<I>expression1</I> is sufficient to determine the return value ofthe entire conditional expression.</DL> <DT><B>for</B> <I>name</I> [ [ <B>in</B> [ <I>word ...</I> ] ] ; ] <B>do</B> <I>list</I> ; <B>done</B><DD>The list of words following <B>in</B> is expanded, generating a listof items.The variable <I>name</I> is set to each element of this listin turn, and <I>list</I> is executed each time.If the <B>in</B> <I>word</I> is omitted, the <B>for</B> command executes<I>list</I> once for each positional parameter that is set (see<FONT SIZE=-1><B>PARAMETERS</B> </FONT>below).The return status is the exit status of the last command that executes.If the expansion of the items following <B>in</B> results in an emptylist, no commands are executed, and the return status is 0.<DT><B>for</B> (( <I>expr1</I> ; <I>expr2</I> ; <I>expr3</I> )) ; <B>do</B> <I>list</I> ; <B>done</B><DD>First, the arithmetic expression <I>expr1</I> is evaluated accordingto the rules described below under<FONT SIZE=-1><B>ARITHMETIC EVALUATION</B>. </FONT>The arithmetic expression <I>expr2</I> is then evaluated repeatedlyuntil it evaluates to zero.Each time <I>expr2</I> evaluates to a non-zero value, <I>list</I> isexecuted and the arithmetic expression <I>expr3</I> is evaluated.If any expression is omitted, it behaves as if it evaluates to 1.The return value is the exit status of the last command in <I>list</I>that is executed, or false if any of the expressions is invalid.<DT><B>select</B> <I>name</I> [ <B>in</B> <I>word</I> ] ; <B>do</B> <I>list</I> ; <B>done</B><DD>The list of words following <B>in</B> is expanded, generating a listof items, and the set of expanded words is printed on the standarderror, each preceded by a number.  If the <B>in</B><I>word</I> is omitted, the positional parameters are printed (see<FONT SIZE=-1><B>PARAMETERS</B> </FONT>below).<B>select</B> then displays the<FONT SIZE=-1><B>PS3</B> </FONT>prompt and reads a line from the standard input.If the line consists of a number corresponding to one ofthe displayed words, then the value of<I>name</I> is set to that word.If the line is empty, the words and prompt are displayed again.If EOF is read, the <B>select</B> command completes and returns 1.Any other value read causes<I>name</I> to be set to null.  The line read is saved in the variable<FONT SIZE=-1><B>REPLY</B>. </FONT>The<I>list</I> is executed after each selection until a<B>break</B> command is executed.The exit status of<B>select</B> is the exit status of the last command executed in<I>list</I>, or zero if no commands were executed.<DT><B>case</B> <I>word</I> <B>in</B> [ [(] <I>pattern</I> [ <B>|</B> <I>pattern</I> ] <DD>A <B>case</B> command first expands <I>word</I>, and tries to matchit against each <I>pattern</I> in turn, using the matching rulesdescribed under<B>Pattern Matching</B> below.The <I>word</I> is expanded using tildeexpansion, parameter and variable expansion, arithmetic expansion,command substitution, process substitution and quote removal.Each <I>pattern</I> examined is expanded using tildeexpansion, parameter and variable expansion, arithmetic expansion,command substitution, process substitution, and quote removal.If the<B>nocasematch</B> shell option is enabled, the match is performed without regard to the caseof alphabetic characters.When a match is found, the corresponding <I>list</I> is executed.If the <B>;;</B> operator is used, no subsequent matches are attempted afterthe first pattern match.Using <B>;&amp;</B> in place of <B>;;</B> causes execution to continue withthe <I>list</I> associated with the next set of patterns.Using <B>;;&amp;</B> in place of <B>;;</B> causes the shell to test the nextpattern list in the statement, if any, and execute any associated <I>list</I>on a successful match,continuing the case statement execution as if the pattern list had not matched.The exit status is zero if nopattern matches.  Otherwise, it is the exit status of thelast command executed in <I>list</I>.<DT><B>if</B> <I>list</I>; <B>then</B> <I>list</I>; [ <B>elif</B> <I>list</I>; <B>then</B> <I>list</I>; ] ... [ <B>else</B> <I>list</I>; ] <B>fi</B><DD>The<B>if</B> <I>list</I> is executed.  If its exit status is zero, the<B>then</B> <I>list</I> is executed.  Otherwise, each <B>elif</B><I>list</I> is executed in turn, and if its exit status is zero,the corresponding <B>then</B> <I>list</I> is executed and thecommand completes.  Otherwise, the <B>else</B> <I>list</I> isexecuted, if present.  The exit status is the exit status of thelast command executed, or zero if no condition tested true.<DT><B>while</B> <I>list-1</I>; <B>do</B> <I>list-2</I>; <B>done</B><DD> <DT><B>until</B> <I>list-1</I>; <B>do</B> <I>list-2</I>; <B>done</B><DD> The <B>while</B> command continuously executes the list<I>list-2</I> as long as the last command in the list <I>list-1</I> returnsan exit status of zero.  The <B>until</B> command is identicalto the <B>while</B> command, except that the test is negated:<I>list-2</I> is executed as long as the last command in<I>list-1</I> returns a non-zero exit status.The exit status of the <B>while</B> and <B>until</B> commandsis the exit statusof the last command executed in <I>list-2</I>, or zero ifnone was executed.</DL><A NAME="lbAP">&nbsp;</A><H4>Coprocesses</H4> A <I>coprocess</I> is a shell command preceded by the <B>coproc</B> reservedword.A coprocess is executed asynchronously in a subshell, as if the commandhad been terminated with the <B>&amp;</B> control operator, with a two-way pipeestablished between the executing shell and the coprocess.<P> The syntax for a coprocess is:<DL COMPACT><DT><DD><P> <B>coproc</B> [<I>NAME</I>] <I>command</I> [<I>redirections</I>]</DL> <P> This creates a coprocess named <I>NAME</I>.<I>command</I> may be either a simple command or a compoundcommand (see above).<I>NAME</I> is a shell variable name.If <I>NAME</I> is not supplied, the default name is <B>COPROC</B>.<P> The recommended form to use for a coprocess is<DL COMPACT><DT><DD><P> <B>coproc</B> <I>NAME</I> { <I>command</I> [<I>redirections</I>]; }</DL> <P> This form is recommended because simple commands result in the coprocessalways being named <B>COPROC</B>, and it is simpler to use and more completethan the other compound commands.<P> If <I>command</I> is a compound command, <I>NAME</I> is optional. Theword following <B>coproc</B> determines whether that word is interpretedas a variable name: it is interpreted as <I>NAME</I> if it is not areserved word that introduces a compound command.If <I>command</I> is a simple command, <I>NAME</I> is not allowed; thisis to avoid confusion between <I>NAME</I> and the first word of the simplecommand.<P> When the coprocess is executed, the shell creates an array variable (see<B>Arrays</B> below) named <I>NAME</I> in the context of the executing shell.The standard output of<I>command</I> is connected via a pipe to a file descriptor in the executing shell,and that file descriptor is assigned to <I>NAME</I>[0].The standard input of<I>command</I> is connected via a pipe to a file descriptor in the executing shell,and that file descriptor is assigned to <I>NAME</I>[1].This pipe is established before any redirections specified by thecommand (see<FONT SIZE=-1><B>REDIRECTION</B> </FONT>below).The file descriptors can be utilized as arguments to shell commandsand redirections using standard word expansions.Other than those created to execute command and process substitutions,the file descriptors are not available in subshells.<P> The process ID of the shell spawned to execute the coprocess isavailable as the value of the variable <I>NAME</I>_PID.The <B>wait</B>builtin command may be used to wait for the coprocess to terminate.<P> Since the coprocess is created as an asynchronous command,the <B>coproc</B> command always returns success.The return status of a coprocess is the exit status of <I>command</I>.<A NAME="lbAQ">&nbsp;</A><H4>Shell Function Definitions</H4> A shell function is an object that is called like a simple command andexecutes a compound command with a new set of positional parameters.Shell functions are declared as follows:<DL COMPACT><DT><I>fname</I> () <I>compound-command</I> [<I>redirection</I>]<DD> <DT><B>function</B> <I>fname</I> [()] <I>compound-command</I> [<I>redirection</I>]<DD> This defines a function named <I>fname</I>.The reserved word <B>function</B> is optional.If the <B>function</B> reserved word is supplied, the parentheses are optional.The <I>body</I> of the function is the compound command<I>compound-command</I> (see <B>Compound Commands</B> above).That command is usually a <I>list</I> of commands between { and }, butmay be any command listed under <B>Compound Commands</B> above.If the <B>function</B> reserved word is used, but theparentheses are not supplied, the braces are recommended.<I>compound-command</I> is executed whenever <I>fname</I> is specified as thename of a simple command.When in <I>posix mode</I>, <I>fname</I> must be a valid shell <I>name</I>and may not be the name of one of thePOSIX <I>special builtins</I>.In default mode, a function name can be any unquoted shell word that doesnot contain <B>$</B>.Any redirections (see<FONT SIZE=-1><B>REDIRECTION</B> </FONT>below) specified when a function is defined are performedwhen the function is executed.The exit status of a function definition is zero unless a syntax erroroccurs or a readonly function with the same name already exists.When executed, the exit status of a function is the exit status of thelast command executed in the body.  (See<FONT SIZE=-1><B>FUNCTIONS</B> </FONT>below.)</DL><A NAME="lbAR">&nbsp;</A><H3>COMMENTS</H3> In a non-interactive shell, or an interactive shell in which the<B>interactive_comments</B> option to the<B>shopt</B> builtin is enabled (see<FONT SIZE=-1><B>SHELL BUILTIN COMMANDS</B> </FONT>below), a word beginning with<B>#</B> causes that word and all remaining characters on that line tobe ignored.  An interactive shell without the<B>interactive_comments</B> option enabled does not allow comments.  The<B>interactive_comments</B> option is on by default in interactive shells.<A NAME="lbAS">&nbsp;</A><H3>QUOTING</H3> <I>Quoting</I> is used to remove the special meaning of certaincharacters or words to the shell.  Quoting can be used todisable special treatment for special characters, to preventreserved words from being recognized as such, and to preventparameter expansion.<P> Each of the <I>metacharacters</I> listed above under<FONT SIZE=-1><B>DEFINITIONS</B> </FONT>has special meaning to the shell and must be quoted if it is torepresent itself.<P> When the command history expansion facilities are being used(see<FONT SIZE=-1><B>HISTORY EXPANSION</B> </FONT>below), the<I>history expansion</I> character, usually <B>!</B>, must be quotedto prevent history expansion.<P> There are three quoting mechanisms: the<I>escape character</I>, single quotes, and double quotes.<P> A non-quoted backslash (<B>\</B>) is the<I>escape character</I>. It preserves the literal value of the next character that follows,with the exception of &lt;newline&gt;.  If a <B>\</B>&lt;newline&gt; pairappears, and the backslash is not itself quoted, the <B>\</B>&lt;newline&gt;is treated as a line continuation (that is, it is removed from theinput stream and effectively ignored).<P> Enclosing characters in single quotes preserves the literal valueof each character within the quotes.  A single quote may not occurbetween single quotes, even when preceded by a backslash.<P> Enclosing characters in double quotes preserves the literal valueof all characters within the quotes, with the exception of<B>$</B>, <B>`</B>, <B>\</B>, and, when history expansion is enabled,<B>!</B>. When the shell is in <I>posix mode</I>, the <B>!</B> has no special meaningwithin double quotes, even when history expansion is enabled.The characters<B>$</B> and<B>`</B> retain their special meaning within double quotes.  The backslashretains its special meaning only when followed by one of the followingcharacters:<B>$</B>, <B>`</B>, <B>&quot;</B>,<B>\</B>, or<B>&lt;newline&gt;</B>. A double quote may be quoted within double quotes by preceding it witha backslash.If enabled, history expansion will be performed unless an<B>!</B> appearing in double quotes is escaped using a backslash.The backslash preceding the<B>!</B> is not removed.<P> The special parameters<B>*</B> and<B>@</B> have special meaning when in doublequotes (see<FONT SIZE=-1><B>PARAMETERS</B> </FONT>below).<P> Character sequences of the form <B>$</B>aq<I>string</I>aq are treatedas a special variant of single quotes.The sequence expands to <I>string</I>, with backslash-escaped charactersin <I>string</I> replaced as specified by the ANSI C standard.Backslash escape sequences, if present, are decoded as follows:<DL COMPACT><DT><DD> <DL COMPACT><DT><B>\a</B> <DD>alert (bell)<DT><B>\b</B> <DD>backspace<DT><B>\e</B> <DD><DT><B>\E</B> <DD>an escape character<DT><B>\f</B> <DD>form feed<DT><B>\n</B> <DD>new line<DT><B>\r</B> <DD>carriage return<DT><B>\t</B> <DD>horizontal tab<DT><B>\v</B> <DD>vertical tab<DT><B>\\</B> <DD>backslash<DT><B>\aq</B> <DD>single quote<DT><B>\dq</B> <DD>double quote<DT><B>\?</B> <DD>question mark<DT><B>\</B><I>nnn</I> <DD>the eight-bit character whose value is the octal value <I>nnn</I>(one to three octal digits)<DT><B>\x</B><I>HH</I> <DD>the eight-bit character whose value is the hexadecimal value <I>HH</I>(one or two hex digits)<DT><B>\u</B><I>HHHH</I> <DD>the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value<I>HHHH</I> (one to four hex digits)<DT><B>\U</B><I>HHHHHHHH</I> <DD>the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value<I>HHHHHHHH</I> (one to eight hex digits)<DT><B>\c</B><I>x</I> <DD>a control-<I>x</I> character </DL></DL> <P> The expanded result is single-quoted, as if the dollar sign hadnot been present.<P> A double-quoted string preceded by a dollar sign (<B>$</B>dq<I>string</I>dq)will cause the string to be translated according to the current locale.The <I>gettext</I> infrastructure performs the lookup andtranslation, using the <B>LC_MESSAGES</B>, <B>TEXTDOMAINDIR</B>,and <B>TEXTDOMAIN</B> shell variables.If the current locale is <B>C</B> or <B>POSIX</B>,if there are no translations available,or if the string is not translated,the dollar sign is ignored.This is a form of double quoting, so the string remains double-quotedby default, whether or not it is translated and replaced.If the <B>noexpand_translation</B> option is enabledusing the <B>shopt</B> builtin,translated strings are single-quoted instead of double-quoted.See the description of<B>shopt</B> below under<FONT SIZE=-1><B>SHELL</B>BUILTIN<B>COMMANDS</B>. </FONT><A NAME="lbAT">&nbsp;</A><H3>PARAMETERS</H3> A<I>parameter</I> is an entity that stores values.It can be a<I>name</I>, a number, or one of the special characters listed below under<B>Special Parameters</B>. A<I>variable</I> is a parameter denoted by a<I>name</I>. A variable has a <I>value</I> and zero or more <I>attributes</I>.Attributes are assigned using the<B>declare</B> builtin command (see<B>declare</B> below in<FONT SIZE=-1><B>SHELL BUILTIN COMMANDS</B>). </FONT><P> A parameter is set if it has been assigned a value.  The null string isa valid value.  Once a variable is set, it may be unset only by usingthe<B>unset</B> builtin command (see<FONT SIZE=-1><B>SHELL BUILTIN COMMANDS</B> </FONT>below).<P> A<I>variable</I> may be assigned to by a statement of the form<DL COMPACT><DT><DD><P> <I>name</I>=[<I>value</I>]</DL> <P> If<I>value</I> is not given, the variable is assigned the null string.  All<I>values</I> undergo tilde expansion, parameter and variable expansion,command substitution, arithmetic expansion, and quoteremoval (see<FONT SIZE=-1><B>EXPANSION</B> </FONT>below).  If the variable has its<B>integer</B> attribute set, then<I>value</I> is evaluated as an arithmetic expression even if the $((...)) expansion isnot used (see<B>Arithmetic Expansion</B> below).Word splitting and pathname expansion are not performed.Assignment statements may also appear as arguments to the<B>alias</B>, <B>declare</B>, <B>typeset</B>, <B>export</B>, <B>readonly</B>, and<B>local</B> builtin commands (<I>declaration</I> commands).When in <I>posix mode</I>, these builtins may appear in a command afterone or more instances of the <B>command</B> builtin and retain theseassignment statement properties.<P> In the context where an assignment statement is assigning a valueto a shell variable or array index, the += operator can be used toappend to or add to the variable's previous value.This includes arguments to builtin commands such as <B>declare</B> thataccept assignment statements (<I>declaration</I> commands).When += is applied to a variable for which the <B>integer</B> attribute has beenset, <I>value</I> is evaluated as an arithmetic expression and added to thevariable's current value, which is also evaluated.When += is applied to an array variable using compound assignment (see<B>Arrays</B> below), thevariable's value is not unset (as it is when using =), and new values areappended to the array beginning at one greater than the array's maximum index(for indexed arrays) or added as additional key-value pairs in anassociative array.When applied to a string-valued variable, <I>value</I> is expanded andappended to the variable's value.<P> A variable can be assigned the <I>nameref</I> attribute using the<B>-n</B> option to the <B>declare</B> or <B>local</B> builtin commands(see the descriptions of <B>declare</B> and <B>local</B> below)to create a <I>nameref</I>, or a reference to another variable.This allows variables to be manipulated indirectly.Whenever the nameref variable is referenced, assigned to, unset, or hasits attributes modified (other than using or changing the <I>nameref</I>attribute itself), theoperation is actually performed on the variable specified by the namerefvariable's value.A nameref is commonly used within shell functions to refer to a variablewhose name is passed as an argument to the function.For instance, if a variable name is passed to a shell function as its firstargument, running<P><DL COMPACT><DT><DD><TT>declare -n ref=$1</TT> </DL> <P>inside the function creates a nameref variable <B>ref</B> whose value isthe variable name passed as the first argument.References and assignments to <B>ref</B>, and changes to its attributes,are treated as references, assignments, and attribute modificationsto the variable whose name was passed as <B>$1</B>.If the control variable in a <B>for</B> loop has the nameref attribute,the list of words can be a list of shell variables, and a name referencewill be established for each word in the list, in turn, when the loop isexecuted.Array variables cannot be given the <B>nameref</B> attribute.However, nameref variables can reference array variables and subscriptedarray variables.Namerefs can be unset using the <B>-n</B> option to the <B>unset</B> builtin.Otherwise, if <B>unset</B> is executed with the name of a nameref variableas an argument, the variable referenced by the nameref variable will be unset.<A NAME="lbAU">&nbsp;</A><H4>Positional Parameters</H4> A<I>positional parameter</I> is a parameter denoted by one or moredigits, other than the single digit 0.  Positional parameters areassigned from the shell's arguments when it is invoked,and may be reassigned using the<B>set</B> builtin command.  Positional parameters may not be assigned towith assignment statements.  The positional parameters aretemporarily replaced when a shell function is executed (see<FONT SIZE=-1><B>FUNCTIONS</B> </FONT>below).<P> When a positional parameter consisting of more than a singledigit is expanded, it must be enclosed in braces (see<FONT SIZE=-1><B>EXPANSION</B> </FONT>below).<A NAME="lbAV">&nbsp;</A><H4>Special Parameters</H4> The shell treats several parameters specially.  These parameters mayonly be referenced; assignment to them is not allowed. <DL COMPACT><DT><B>*</B> <DD>Expands to the positional parameters, starting from one.When the expansion is not within double quotes, each positional parameterexpands to a separate word.In contexts where it is performed, those wordsare subject to further word splitting and pathname expansion.When the expansion occurs within double quotes, it expands to a single wordwith the value of each parameter separated by the first character of the<FONT SIZE=-1><B>IFS</B> </FONT>special variable.  That is, &quot;<B>$*</B>&quot; is equivalentto &quot;<B>$1</B><I>c</I><B>$2</B><I>c</I><B>...</B>&quot;, where<I>c</I> is the first character of the value of the<FONT SIZE=-1><B>IFS</B> </FONT>variable.  If<FONT SIZE=-1><B>IFS</B> </FONT>is unset, the parameters are separated by spaces.If<FONT SIZE=-1><B>IFS</B> </FONT>is null, the parameters are joined without intervening separators.<DT><B>@</B> <DD>Expands to the positional parameters, starting from one.In contexts where word splitting is performed, this expands eachpositional parameter to a separate word; if not within doublequotes, these words are subject to word splitting.In contexts where word splitting is not performed,this expands to a single wordwith each positional parameter separated by a space.When theexpansion occurs within double quotes, each parameter expands to aseparate word.  That is, &quot;<B>$@</B>&quot; is equivalent to&quot;<B>$1</B>&quot; &quot;<B>$2</B>&quot; ...If the double-quoted expansion occurs within a word, the expansion ofthe first parameter is joined with the beginning part of the originalword, and the expansion of the last parameter is joined with the lastpart of the original word.When there are no positional parameters, &quot;<B>$@</B>&quot; and<B>$@</B> expand to nothing (i.e., they are removed).<DT><B>#</B> <DD>Expands to the number of positional parameters in decimal.<DT><B>?</B> <DD>Expands to the exit status of the most recently executed foregroundpipeline.<DT><B>-</B> <DD>Expands to the current option flags as specified upon invocation,by the<B>set</B> builtin command, or those set by the shell itself(such as the<B>-i</B> option).<DT><B>$</B> <DD>Expands to the process ID of the shell. In a subshell, itexpands to the process ID of the current shell, not thesubshell.<DT><B>!</B> <DD>Expands to the process ID of the job most recently placed into thebackground, whether executed as an asynchronous command or usingthe <B>bg</B> builtin (see<FONT SIZE=-1><B>JOB CONTROL</B> </FONT>below).<DT><B>0</B> <DD>Expands to the name of the shell or shell script.  This is set atshell initialization.  If<B>bash</B> is invoked with a file of commands,<B>$0</B> is set to the name of that file.  If<B>bash</B> is started with the<B>-c</B> option, then<B>$0</B> is set to the first argument after the string to beexecuted, if one is present.  Otherwise, it is setto the filename used to invoke<B>bash</B>, as given by argument zero. </DL><A NAME="lbAW">&nbsp;</A><H4>Shell Variables</H4> The following variables are set by the shell:<P>  <DL COMPACT><DT><B>_</B> <DD>At shell startup, set to the pathname used to invoke theshell or shell script being executed as passed in the environmentor argument list.Subsequently, expands to the last argument to the previous simplecommand executed in the foreground, after expansion.Also set to the full pathname used to invoke each command executedand placed in the environment exported to that command.When checking mail, this parameter holds the name of the mail filecurrently being checked.<DT><B>BASH</B> <DD>Expands to the full filename used to invoke this instance of<B>bash</B>. <DT><B>BASHOPTS</B> <DD>A colon-separated list of enabled shell options.  Each word inthe list is a valid argument for the<B>-s</B> option to the<B>shopt</B> builtin command (see<FONT SIZE=-1><B>SHELL BUILTIN COMMANDS</B> </FONT>below).  The options appearing in<FONT SIZE=-1><B>BASHOPTS</B> </FONT>are those reported as<I>on</I> by <B>shopt</B>.If this variable is in the environment when<B>bash</B> starts up, each shell option in the list will be enabled beforereading any startup files.This variable is read-only.<DT><B>BASHPID</B> <DD>Expands to the process ID of the current <B>bash</B> process.This differs from <B>$$</B> under certain circumstances, such as subshellsthat do not require <B>bash</B> to be re-initialized.Assignments to<FONT SIZE=-1><B>BASHPID</B> </FONT>have no effect.If<B>BASHPID</B> is unset, it loses its special properties, even if it issubsequently reset.<DT><B>BASH_ALIASES</B> <DD>An associative array variable whose members correspond to the internallist of aliases as maintained by the <B>alias</B> builtin.Elements added to this array appear in the alias list; however,unsetting array elements currently does not cause aliases to be removedfrom the alias list.If<B>BASH_ALIASES</B> is unset, it loses its special properties, even if it issubsequently reset.<DT><B>BASH_ARGC</B> <DD>An array variable whose values are the number of parameters in eachframe of the current <B>bash</B> execution call stack.The number ofparameters to the current subroutine (shell function or script executedwith <B>.</B> or <B>source</B>) is at the top of the stack.When a subroutine is executed, the number of parameters passed is pushed onto<FONT SIZE=-1><B>BASH_ARGC</B>. </FONT>The shell sets<FONT SIZE=-1><B>BASH_ARGC</B> </FONT>only when in extended debugging mode (see the description of the<B>extdebug</B> option to the<B>shopt</B> builtin below).Setting <B>extdebug</B> after the shell has started to execute a script,or referencing this variable when <B>extdebug</B> is not set,may result in inconsistent values.<DT><B>BASH_ARGV</B> <DD>An array variable containing all of the parameters in the current <B>bash</B>execution call stack.  The final parameter of the last subroutine callis at the top of the stack; the first parameter of the initial call isat the bottom.  When a subroutine is executed, the parameters suppliedare pushed onto<FONT SIZE=-1><B>BASH_ARGV</B>. </FONT>The shell sets<FONT SIZE=-1><B>BASH_ARGV</B> </FONT>only when in extended debugging mode(see the description of the<B>extdebug</B> option to the<B>shopt</B> builtin below).Setting <B>extdebug</B> after the shell has started to execute a script,or referencing this variable when <B>extdebug</B> is not set,may result in inconsistent values.<DT><B>BASH_ARGV0</B> <DD>When referenced, this variable expands to the name of the shell or shellscript (identical to<B>$0</B>; see the description of special parameter 0 above).Assignment to<B>BASH_ARGV0</B> causes the value assigned to also be assigned to <B>$0</B>.If<B>BASH_ARGV0</B> is unset, it loses its special properties, even if it issubsequently reset.<DT><B>BASH_CMDS</B> <DD>An associative array variable whose members correspond to the internalhash table of commands as maintained by the <B>hash</B> builtin.Elements added to this array appear in the hash table; however,unsetting array elements currently does not cause command names to be removedfrom the hash table.If<B>BASH_CMDS</B> is unset, it loses its special properties, even if it issubsequently reset.<DT><B>BASH_COMMAND</B> <DD>The command currently being executed or about to be executed, unless theshell is executing a command as the result of a trap,in which case it is the command executing at the time of the trap.If<B>BASH_COMMAND</B> is unset, it loses its special properties, even if it issubsequently reset.<DT><B>BASH_EXECUTION_STRING</B> <DD>The command argument to the <B>-c</B> invocation option.<DT><B>BASH_LINENO</B> <DD>An array variable whose members are the line numbers in source fileswhere each corresponding member of<FONT SIZE=-1><B>FUNCNAME</B> </FONT>was invoked.<B>${BASH_LINENO[</B><I>$i</I><B>]}</B> is the line number in the sourcefile (<B>${BASH_SOURCE[</B><I>$i+1</I><B>]}</B>) where<B>${FUNCNAME[</B><I>$i</I><B>]}</B> was called(or <B>${BASH_LINENO[</B><I>$i-1</I><B>]}</B> if referenced within anothershell function).Use<FONT SIZE=-1><B>LINENO</B> </FONT>to obtain the current line number.<DT><B>BASH_LOADABLES_PATH</B> <DD>A colon-separated list of directories in which the shell looks fordynamically loadable builtins specified by the<B>enable</B> command.<DT><B>BASH_REMATCH</B> <DD>An array variable whose members are assigned by the <B>=~</B> binaryoperator to the <B>[[</B> conditional command.The element with index 0 is the portion of the stringmatching the entire regular expression.The element with index <I>n</I> is the portion of thestring matching the <I>n</I>th parenthesized subexpression.<DT><B>BASH_SOURCE</B> <DD>An array variable whose members are the source filenameswhere the corresponding shell function names in the<FONT SIZE=-1><B>FUNCNAME</B> </FONT>array variable are defined.The shell function<B>${FUNCNAME[</B><I>$i</I><B>]}</B> is defined in the file<B>${BASH_SOURCE[</B><I>$i</I><B>]}</B> and called from<B>${BASH_SOURCE[</B><I>$i+1</I><B>]}</B>.<DT><B>BASH_SUBSHELL</B> <DD>Incremented by one within each subshell or subshell environment whenthe shell begins executing in that environment.The initial value is 0.If<B>BASH_SUBSHELL</B> is unset, it loses its special properties, even if it issubsequently reset.<DT><B>BASH_VERSINFO</B> <DD>A readonly array variable whose members hold version information forthis instance of<B>bash</B>. The values assigned to the array members are as follows:<P><DL COMPACT><DT><DD><DL COMPACT><DT><B>BASH_VERSINFO[</B>0] <DD>The major version number (the <I>release</I>).<DT><B>BASH_VERSINFO[</B>1] <DD>The minor version number (the <I>version</I>).<DT><B>BASH_VERSINFO[</B>2] <DD>The patch level.<DT><B>BASH_VERSINFO[</B>3] <DD>The build version.<DT><B>BASH_VERSINFO[</B>4] <DD>The release status (e.g., <I>beta1</I>).<DT><B>BASH_VERSINFO[</B>5] <DD>The value of<FONT SIZE=-1><B>MACHTYPE</B>. </FONT></DL></DL> <DT><B>BASH_VERSION</B> <DD>Expands to a string describing the version of this instance of<B>bash</B>. <DT><B>COMP_CWORD</B> <DD>An index into <B>${COMP_WORDS}</B> of the word containing the currentcursor position.This variable is available only in shell functions invoked by theprogrammable completion facilities (see <B>Programmable Completion</B>below).<DT><B>COMP_KEY</B> <DD>The key (or final key of a key sequence) used to invoke the currentcompletion function.<DT><B>COMP_LINE</B> <DD>The current command line.This variable is available only in shell functions and externalcommands invoked by theprogrammable completion facilities (see <B>Programmable Completion</B>below).<DT><B>COMP_POINT</B> <DD>The index of the current cursor position relative to the beginning ofthe current command.If the current cursor position is at the end of the current command,the value of this variable is equal to <B>${#COMP_LINE}</B>.This variable is available only in shell functions and externalcommands invoked by theprogrammable completion facilities (see <B>Programmable Completion</B>below).<DT><B>COMP_TYPE</B> <DD>Set to an integer value corresponding to the type of completion attemptedthat caused a completion function to be called:<I>TAB</I>, for normal completion,<I>?</I>, for listing completions after successive tabs,<I>!</I>, for listing alternatives on partial word completion,<I>@</I>, to list completions if the word is not unmodified,or<I>%</I>, for menu completion.This variable is available only in shell functions and externalcommands invoked by theprogrammable completion facilities (see <B>Programmable Completion</B>below).<DT><B>COMP_WORDBREAKS</B> <DD>The set of characters that the <B>readline</B> library treats as wordseparators when performing word completion.If<FONT SIZE=-1><B>COMP_WORDBREAKS</B> </FONT>is unset, it loses its special properties, even if it issubsequently reset.<DT><B>COMP_WORDS</B> <DD>An array variable (see <B>Arrays</B> below) consisting of the individualwords in the current command line.The line is split into words as <B>readline</B> would split it, using<FONT SIZE=-1><B>COMP_WORDBREAKS</B> </FONT>as described above.This variable is available only in shell functions invoked by theprogrammable completion facilities (see <B>Programmable Completion</B>below).<DT><B>COPROC</B> <DD>An array variable (see <B>Arrays</B> below) created to hold the file descriptorsfor output from and input to an unnamed coprocess (see <B>Coprocesses</B>above).<DT><B>DIRSTACK</B> <DD>An array variable (see<B>Arrays</B> below) containing the current contents of the directory stack.Directories appear in the stack in the order they are displayed by the<B>dirs</B> builtin.Assigning to members of this array variable may be used to modifydirectories already in the stack, but the<B>pushd</B> and<B>popd</B> builtins must be used to add and remove directories.Assignment to this variable will not change the current directory.If<FONT SIZE=-1><B>DIRSTACK</B> </FONT>is unset, it loses its special properties, even if it issubsequently reset.<DT><B>EPOCHREALTIME</B> <DD>Each time this parameter is referenced, it expands to the number of secondssince the Unix Epoch (see <I>time</I>(3)) as a floating point valuewith micro-second granularity.Assignments to<FONT SIZE=-1><B>EPOCHREALTIME</B> </FONT>are ignored.If<FONT SIZE=-1><B>EPOCHREALTIME</B> </FONT>is unset, it loses its special properties, even if it issubsequently reset.<DT><B>EPOCHSECONDS</B> <DD>Each time this parameter is referenced, it expands to the number of secondssince the Unix Epoch (see <I>time</I>(3)).Assignments to<FONT SIZE=-1><B>EPOCHSECONDS</B> </FONT>are ignored.If<FONT SIZE=-1><B>EPOCHSECONDS</B> </FONT>is unset, it loses its special properties, even if it issubsequently reset.<DT><B>EUID</B> <DD>Expands to the effective user ID of the current user, initialized atshell startup.  This variable is readonly.<DT><B>FUNCNAME</B> <DD>An array variable containing the names of all shell functionscurrently in the execution call stack.The element with index 0 is the name of any currently-executingshell function.The bottom-most element (the one with the highest index) is<TT>&quot;main&quot;</TT>. This variable exists only when a shell function is executing.Assignments to<FONT SIZE=-1><B>FUNCNAME</B> </FONT>have no effect.If<FONT SIZE=-1><B>FUNCNAME</B> </FONT>is unset, it loses its special properties, even if it issubsequently reset.<P>  This variable can be used with <B>BASH_LINENO</B> and <B>BASH_SOURCE</B>.Each element of <B>FUNCNAME</B> has corresponding elements in<B>BASH_LINENO</B> and <B>BASH_SOURCE</B> to describe the call stack.For instance, <B>${FUNCNAME[</B><I>$i</I><B>]}</B> was called from the file<B>${BASH_SOURCE[</B><I>$i+1</I><B>]}</B> at line number<B>${BASH_LINENO[</B><I>$i</I><B>]}</B>.The <B>caller</B> builtin displays the current call stack using thisinformation.<DT><B>GROUPS</B> <DD>An array variable containing the list of groups of which the currentuser is a member.Assignments to<FONT SIZE=-1><B>GROUPS</B> </FONT>have no effect.If<FONT SIZE=-1><B>GROUPS</B> </FONT>is unset, it loses its special properties, even if it issubsequently reset.<DT><B>HISTCMD</B> <DD>The history number, or index in the history list, of the currentcommand.Assignments to<FONT SIZE=-1><B>HISTCMD</B> </FONT>are ignored.If<FONT SIZE=-1><B>HISTCMD</B> </FONT>is unset, it loses its special properties, even if it issubsequently reset.<DT><B>HOSTNAME</B> <DD>Automatically set to the name of the current host.<DT><B>HOSTTYPE</B> <DD>Automatically set to a string that uniquelydescribes the type of machine on which<B>bash</B> is executing.The default is system-dependent.<DT><B>LINENO</B> <DD>Each time this parameter is referenced, the shell substitutesa decimal number representing the current sequential line number(starting with 1) within a script or function.  When not in ascript or function, the value substituted is not guaranteed tobe meaningful.If<FONT SIZE=-1><B>LINENO</B> </FONT>is unset, it loses its special properties, even if it issubsequently reset.<DT><B>MACHTYPE</B> <DD>Automatically set to a string that fully describes the systemtype on which<B>bash</B> is executing, in the standard GNU <I>cpu-company-system</I> format.The default is system-dependent.<DT><B>MAPFILE</B> <DD>An array variable (see <B>Arrays</B> below) created to hold the textread by the <B>mapfile</B> builtin when no variable name is supplied.<DT><B>OLDPWD</B> <DD>The previous working directory as set by the<B>cd</B> command.<DT><B>OPTARG</B> <DD>The value of the last option argument processed by the<B>getopts</B> builtin command (see<FONT SIZE=-1><B>SHELL BUILTIN COMMANDS</B> </FONT>below).<DT><B>OPTIND</B> <DD>The index of the next argument to be processed by the<B>getopts</B> builtin command (see<FONT SIZE=-1><B>SHELL BUILTIN COMMANDS</B> </FONT>below).<DT><B>OSTYPE</B> <DD>Automatically set to a string thatdescribes the operating system on which<B>bash</B> is executing.The default is system-dependent.<DT><B>PIPESTATUS</B> <DD>An array variable (see<B>Arrays</B> below) containing a list of exit status values from the processesin the most-recently-executed foreground pipeline (which maycontain only a single command).<DT><B>PPID</B> <DD>The process ID of the shell's parent.  This variable is readonly.<DT><B>PWD</B> <DD>The current working directory as set by the<B>cd</B> command.<DT><B>RANDOM</B> <DD>Each time this parameter is referenced, it expands to a random integerbetween 0 and 32767.Assigninga value to<FONT SIZE=-1><B>RANDOM</B> </FONT>initializes (seeds) the sequence of random numbers.If<FONT SIZE=-1><B>RANDOM</B> </FONT>is unset, it loses its special properties, even if it issubsequently reset.<DT><B>READLINE_ARGUMENT</B> <DD>Any numeric argument given to a readline command that was defined using<TT>bind -x</TT> (see<FONT SIZE=-1><B>SHELL BUILTIN COMMANDS</B> </FONT>below)when it was invoked.<DT><B>READLINE_LINE</B> <DD>The contents of the<B>readline</B> line buffer, for use with<TT>bind -x</TT> (see<FONT SIZE=-1><B>SHELL BUILTIN COMMANDS</B> </FONT>below).<DT><B>READLINE_MARK</B> <DD>The position of the mark (saved insertion point) in the<B>readline</B> line buffer, for use with<TT>bind -x</TT> (see<FONT SIZE=-1><B>SHELL BUILTIN COMMANDS</B> </FONT>below).The characters between the insertion point and the mark are oftencalled the <I>region</I>.<DT><B>READLINE_POINT</B> <DD>The position of the insertion point in the<B>readline</B> line buffer, for use with<TT>bind -x</TT> (see<FONT SIZE=-1><B>SHELL BUILTIN COMMANDS</B> </FONT>below).<DT><B>REPLY</B> <DD>Set to the line of input read by the<B>read</B> builtin command when no arguments are supplied.<DT><B>SECONDS</B> <DD>Each time this parameter isreferenced, it expands to the number of seconds since shell invocation.If a value is assigned to<FONT SIZE=-1><B>SECONDS</B>, </FONT>the value returned upon subsequentreferences isthe number of seconds since the assignment plus the value assigned.The number of seconds at shell invocation and the current time are alwaysdetermined by querying the system clock.If<FONT SIZE=-1><B>SECONDS</B> </FONT>is unset, it loses its special properties, even if it issubsequently reset.<DT><B>SHELLOPTS</B> <DD>A colon-separated list of enabled shell options.  Each word inthe list is a valid argument for the<B>-o</B> option to the<B>set</B> builtin command (see<FONT SIZE=-1><B>SHELL BUILTIN COMMANDS</B> </FONT>below).  The options appearing in<FONT SIZE=-1><B>SHELLOPTS</B> </FONT>are those reported as<I>on</I> by <B>set -o</B>.If this variable is in the environment when<B>bash</B> starts up, each shell option in the list will be enabled beforereading any startup files.This variable is read-only.<DT><B>SHLVL</B> <DD>Incremented by one each time an instance of<B>bash</B> is started.<DT><B>SRANDOM</B> <DD>This variable expands to a 32-bit pseudo-random number each time it isreferenced. The random number generator is not linear on systems thatsupport <TT>/dev/urandom</TT> or <I>arc4random</I>, so each returned numberhas no relationship to the numbers preceding it.The random number generator cannot be seeded, so assignments to thisvariable have no effect.If<FONT SIZE=-1><B>SRANDOM</B> </FONT>is unset, it loses its special properties,even if it is subsequently reset.<DT><B>UID</B> <DD>Expands to the user ID of the current user, initialized at shell startup.This variable is readonly. </DL><P> The following variables are used by the shell.  In some cases,<B>bash</B> assigns a default value to a variable; these cases are notedbelow.<P>  <DL COMPACT><DT><B>BASH_COMPAT</B> <DD>The value is used to set the shell's compatibility level.See<FONT SIZE=-1><B>SHELL COMPATIBILITY MODE</B> </FONT>below for a description of the various compatibilitylevels and their effects.The value may be a decimal number (e.g., 4.2) or an integer (e.g., 42)corresponding to the desired compatibility level.If <B>BASH_COMPAT</B> is unset or set to the empty string, the compatibilitylevel is set to the default for the current version.If <B>BASH_COMPAT</B> is set to a value that is not one of the validcompatibility levels, the shell prints an error message and sets thecompatibility level to the default for the current version.The valid values correspond to the compatibility levelsdescribed below under<FONT SIZE=-1><B>SHELL COMPATIBILITY MODE</B>. </FONT>For example, 4.2 and 42 are valid values that correspondto the <B>compat42</B> <B>shopt</B> optionand set the compatibility level to 42.The current version is also a valid value.<DT><B>BASH_ENV</B> <DD>If this parameter is set when <B>bash</B> is executing a shell script,its value is interpreted as a filename containing commands toinitialize the shell, as in<A HREF="file:~/.bashrc"><I>~/.bashrc</I></A>. The value of<FONT SIZE=-1><B>BASH_ENV</B> </FONT>is subjected to parameter expansion, command substitution, and arithmeticexpansion before being interpreted as a filename.<FONT SIZE=-1><B>PATH</B> </FONT>is not used to search for the resultant filename.<DT><B>BASH_XTRACEFD</B> <DD>If set to an integer corresponding to a valid file descriptor, <B>bash</B>will write the trace output generated when<TT>set -x</TT> is enabled to that file descriptor.The file descriptor is closed when<FONT SIZE=-1><B>BASH_XTRACEFD</B> </FONT>is unset or assigned a new value.Unsetting<FONT SIZE=-1><B>BASH_XTRACEFD</B> </FONT>or assigning it the empty string causes thetrace output to be sent to the standard error.Note that setting<FONT SIZE=-1><B>BASH_XTRACEFD</B> </FONT>to 2 (the standard error filedescriptor) and then unsetting it will result in the standard errorbeing closed.<DT><B>CDPATH</B> <DD>The search path for the<B>cd</B> command.This is a colon-separated list of directories in which the shell looksfor destination directories specified by the<B>cd</B> command.A sample value is<TT>&quot;.:~:/usr&quot;</TT>. <DT><B>CHILD_MAX</B> <DD>Set the number of exited child status values for the shell to remember.Bash will not allow this value to be decreased below a POSIX-mandatedminimum, and there is a maximum value (currently 8192) that this maynot exceed.The minimum value is system-dependent.<DT><B>COLUMNS</B> <DD>Used by the <B>select</B> compound command to determine the terminal widthwhen printing selection lists.Automatically set if the<B>checkwinsize</B> option is enabled or in an interactive shell upon receipt of a<FONT SIZE=-1><B>SIGWINCH</B>. </FONT><DT><B>COMPREPLY</B> <DD>An array variable from which <B>bash</B> reads the possible completionsgenerated by a shell function invoked by the programmable completionfacility (see <B>Programmable Completion</B> below).Each array element contains one possible completion.<DT><B>EMACS</B> <DD>If <B>bash</B> finds this variable in the environment when the shell startswith value<TT>t</TT>, it assumes that the shell is running in an Emacs shell buffer and disablesline editing.<DT><B>ENV</B> <DD>Expanded and executed similarly to<FONT SIZE=-1><B>BASH_ENV</B> </FONT>(see <B>INVOCATION</B> above)when an interactive shell is invoked in <I>posix mode</I>.<DT><B>EXECIGNORE</B> <DD>A colon-separated list of shell patterns (see <B>Pattern Matching</B>)defining the list of filenames to be ignored by command search using<B>PATH</B>.Files whose full pathnames match one of these patterns are not consideredexecutable files for the purposes of completion and command executionvia <B>PATH</B> lookup.This does not affect the behavior of the <B>[</B>, <B>test</B>, and <B>[[</B>commands.Full pathnames in the command hash table are not subject to <B>EXECIGNORE</B>.Use this variable to ignore shared library files that have the executablebit set, but are not executable files.The pattern matching honors the setting of the <B>extglob</B> shelloption.<DT><B>FCEDIT</B> <DD>The default editor for the<B>fc</B> builtin command.<DT><B>FIGNORE</B> <DD>A colon-separated list of suffixes to ignore when performingfilename completion (see<FONT SIZE=-1><B>READLINE</B> </FONT>below).A filename whose suffix matches one of the entries in<FONT SIZE=-1><B>FIGNORE</B> </FONT>is excluded from the list of matched filenames.A sample value is<TT>&quot;.o:~&quot;</TT>. <DT><B>FUNCNEST</B> <DD>If set to a numeric value greater than 0, defines a maximum functionnesting level.  Function invocations that exceed this nesting levelwill cause the current command to abort.<DT><B>GLOBIGNORE</B> <DD>A colon-separated list of patterns defining the set of file names tobe ignored by pathname expansion.If a file name matched by a pathname expansion pattern also matches oneof the patterns in<FONT SIZE=-1><B>GLOBIGNORE</B>, </FONT>it is removed from the list of matches.<DT><B>HISTCONTROL</B> <DD>A colon-separated list of values controlling how commands are saved onthe history list.If the list of values includes<I>ignorespace</I>, lines which begin with a<B>space</B> character are not saved in the history list.A value of<I>ignoredups</I> causes lines matching the previous history entry to not be saved.A value of<I>ignoreboth</I> is shorthand for <I>ignorespace</I> and <I>ignoredups</I>.A value of<I>erasedups</I> causes all previous lines matching the current line to be removed fromthe history list before that line is saved.Any value not in the above list is ignored.If<FONT SIZE=-1><B>HISTCONTROL</B> </FONT>is unset, or does not include a valid value,all lines read by the shell parser are saved on the history list,subject to the value of<FONT SIZE=-1><B>HISTIGNORE</B>. </FONT>The second and subsequent lines of a multi-line compound command arenot tested, and are added to the history regardless of the value of<FONT SIZE=-1><B>HISTCONTROL</B>. </FONT><DT><B>HISTFILE</B> <DD>The name of the file in which command history is saved (see<FONT SIZE=-1><B>HISTORY</B> </FONT>below).  The default value is <A HREF="file:~/.bash_history"><I>~/.bash_history</I></A>.  If unset, thecommand history is not saved when a shell exits.<DT><B>HISTFILESIZE</B> <DD>The maximum number of lines contained in the history file.  When thisvariable is assigned a value, the history file is truncated, ifnecessary,to contain no more than that number of lines by removing the oldest entries.The history file is also truncated to this size afterwriting it when a shell exits.If the value is 0, the history file is truncated to zero size.Non-numeric values and numeric values less than zero inhibit truncation.The shell sets the default value to the value of <B>HISTSIZE</B>after reading any startup files.<DT><B>HISTIGNORE</B> <DD>A colon-separated list of patterns used to decide which command linesshould be saved on the history list.  Each pattern is anchored at thebeginning of the line and must match the complete line (no implicit`<B>*</B>' is appended).  Each pattern is tested against the lineafter the checks specified by<FONT SIZE=-1><B>HISTCONTROL</B> </FONT>are applied.In addition to the normal shell pattern matching characters, `<B>&amp;</B>'matches the previous history line.  `<B>&amp;</B>' may be escaped using abackslash; the backslash is removed before attempting a match.The second and subsequent lines of a multi-line compound command arenot tested, and are added to the history regardless of the value of<FONT SIZE=-1><B>HISTIGNORE</B>. </FONT>The pattern matching honors the setting of the <B>extglob</B> shelloption.<DT><B>HISTSIZE</B> <DD>The number of commands to remember in the command history (see<FONT SIZE=-1><B>HISTORY</B> </FONT>below).If the value is 0, commands are not saved in the history list.Numeric values less than zero result in every command being savedon the history list (there is no limit).The shell sets the default value to 500 after reading any startup files.<DT><B>HISTTIMEFORMAT</B> <DD>If this variable is set and not null, its value is used as a format stringfor <I>strftime</I>(3) to print the time stamp associated with each historyentry displayed by the <B>history</B> builtin.If this variable is set, time stamps are written to the history file sothey may be preserved across shell sessions.This uses the history comment character to distinguish timestamps fromother history lines.<DT><B>HOME</B> <DD>The home directory of the current user; the default argument for the<B>cd</B> builtin command.The value of this variable is also used when performing tilde expansion.<DT><B>HOSTFILE</B> <DD>Contains the name of a file in the same format as <I>/etc/hosts</I> that should be read when the shell needs to complete ahostname.The list of possible hostname completions may be changed while theshell is running;the next time hostname completion is attempted after thevalue is changed,<B>bash</B> adds the contents of the new file to the existing list.If<FONT SIZE=-1><B>HOSTFILE</B> </FONT>is set, but has no value, or does not name a readable file,<B>bash</B> attempts to read <I>/etc/hosts</I> to obtain the list of possible hostname completions.When<FONT SIZE=-1><B>HOSTFILE</B> </FONT>is unset, the hostname list is cleared.<DT><B>IFS</B> <DD>The<I>Internal Field Separator</I> that is usedfor word splitting after expansion and tosplit lines into words with the<B>read</B> builtin command.  The default value is``&lt;space&gt;&lt;tab&gt;&lt;newline&gt;''.<DT><B>IGNOREEOF</B> <DD>Controls theaction of an interactive shell on receipt of an<FONT SIZE=-1><B>EOF</B> </FONT>character as the sole input.  If set, the value is the number ofconsecutive<FONT SIZE=-1><B>EOF</B> </FONT>characters which must betyped as the first characters on an input line before<B>bash</B> exits.  If the variable exists but does not have a numeric value, orhas no value, the default value is 10.  If it does not exist,<FONT SIZE=-1><B>EOF</B> </FONT>signifies the end of input to the shell.<DT><B>INPUTRC</B> <DD>The filename for the<B>readline</B> startup file, overriding the default of <A HREF="file:~/.inputrc"><I>~/.inputrc</I></A> (see<FONT SIZE=-1><B>READLINE</B> </FONT>below).<DT><B>INSIDE_EMACS</B> <DD>If this variable appears in the environment when the shell starts,<B>bash</B> assumes that it is running inside an Emacs shell bufferand may disable line editing, depending on the value of <B>TERM</B>.<DT><B>LANG</B> <DD>Used to determine the locale category for any category not specificallyselected with a variable starting with <B>LC_</B>.<DT><B>LC_ALL</B> <DD>This variable overrides the value of<FONT SIZE=-1><B>LANG</B> </FONT>and any other<B>LC_</B> variable specifying a locale category.<DT><B>LC_COLLATE</B> <DD>This variable determines the collation order used when sorting theresults of pathname expansion, and determines the behavior of rangeexpressions, equivalence classes, and collating sequences withinpathname expansion and pattern matching.<DT><B>LC_CTYPE</B> <DD>This variable determines the interpretation of characters and thebehavior of character classes within pathname expansion and patternmatching.<DT><B>LC_MESSAGES</B> <DD>This variable determines the locale used to translate double-quotedstrings preceded by a <B>$</B>.<DT><B>LC_NUMERIC</B> <DD>This variable determines the locale category used for number formatting.<DT><B>LC_TIME</B> <DD>This variable determines the locale category used for data and timeformatting.<DT><B>LINES</B> <DD>Used by the <B>select</B> compound command to determine the column lengthfor printing selection lists.Automatically set if the<B>checkwinsize</B> option is enabled or in an interactive shell upon receipt of a<FONT SIZE=-1><B>SIGWINCH</B>. </FONT><DT><B>MAIL</B> <DD>If this parameter is set to a file or directory name and the<FONT SIZE=-1><B>MAILPATH</B> </FONT>variable is not set,<B>bash</B> informs the user of the arrival of mail in the specified file orMaildir-format directory.<DT><B>MAILCHECK</B> <DD>Specifies howoften (in seconds)<B>bash</B> checks for mail.  The default is 60 seconds.  When it is time to checkfor mail, the shell does so before displaying the primary prompt.If this variable is unset, or set to a value that is not a numbergreater than or equal to zero, the shell disables mail checking.<DT><B>MAILPATH</B> <DD>A colon-separated list of filenames to be checked for mail.The message to be printed when mail arrives in a particular filemay be specified by separating the filename from the message with a `?'.When used in the text of the message, <B>$_</B> expands to the name ofthe current mailfile.Example:<DL COMPACT><DT><DD><P> <B>MAILPATH</B>=aq/var/mail/bfox?&quot;You have mail&quot;:~/shell-mail?&quot;$_ has mail!&quot;aq<P> <B>Bash</B> can be configured to supplya default value for this variable (there is no value by default),but the location of the usermail files that it uses is system dependent (e.g., /var/mail/<B>$USER</B>).</DL> <DT><B>OPTERR</B> <DD>If set to the value 1,<B>bash</B> displays error messages generated by the<B>getopts</B> builtin command (see<FONT SIZE=-1><B>SHELL BUILTIN COMMANDS</B> </FONT>below).<FONT SIZE=-1><B>OPTERR</B> </FONT>is initialized to 1 each time the shell is invoked or a shellscript is executed.<DT><B>PATH</B> <DD>The search path for commands.  Itis a colon-separated list of directories in whichthe shell looks for commands (see<FONT SIZE=-1><B>COMMAND EXECUTION</B> </FONT>below).A zero-length (null) directory name in the value of<FONT SIZE=-1><B>PATH</B> </FONT>indicates the current directory.A null directory name may appear as two adjacent colons, or as an initialor trailing colon.The default path is system-dependent,and is set by the administrator who installs<B>bash</B>. A common value is <TT>/usr/local/bin:/usr/local/sbin:/usr/bin:/usr/sbin:/bin:/sbin</TT>.  <DT><B>POSIXLY_CORRECT</B> <DD>If this variable is in the environment when <B>bash</B> starts, the shellenters <I>posix mode</I> before reading the startup files, as if the<B>--posix</B> invocation option had been supplied.  If it is set while the shell isrunning, <B>bash</B> enables <I>posix mode</I>, as if the command<TT>set -o posix</TT> had been executed.When the shell enters <I>posix mode</I>, it sets this variable if it wasnot already set.<DT><B>PROMPT_COMMAND</B> <DD>If this variable is set, and is an array,the value of each set element is executed as a commandprior to issuing each primary prompt.If this is set but not an array variable, its value is used as a command to execute instead.<DT><B>PROMPT_DIRTRIM</B> <DD>If set to a number greater than zero, the value is used as the number oftrailing directory components to retain when expanding the <B>\w</B> and<B>\W</B> prompt string escapes (see<FONT SIZE=-1><B>PROMPTING</B> </FONT>below).  Characters removed are replaced with an ellipsis.<DT><B>PS0</B> <DD>The value of this parameter is expanded (see<FONT SIZE=-1><B>PROMPTING</B> </FONT>below) and displayed by interactive shells after reading a commandand before the command is executed.<DT><B>PS1</B> <DD>The value of this parameter is expanded (see<FONT SIZE=-1><B>PROMPTING</B> </FONT>below) and used as the primary prompt string.  The default value is``<B>\s-\v\$ </B>''.<DT><B>PS2</B> <DD>The value of this parameter is expanded as with<FONT SIZE=-1><B>PS1</B> </FONT>and used as the secondary prompt string.  The default is``<B>&gt; </B>''.<DT><B>PS3</B> <DD>The value of this parameter is used as the prompt for the<B>select</B> command (see<FONT SIZE=-1><B>SHELL GRAMMAR</B> </FONT>above).<DT><B>PS4</B> <DD>The value of this parameter is expanded as with<FONT SIZE=-1><B>PS1</B> </FONT>and the value is printed before each command<B>bash</B> displays during an execution trace.  The first character ofthe expanded value of<FONT SIZE=-1><B>PS4</B> </FONT>is replicated multiple times, as necessary, to indicate multiplelevels of indirection.  The default is ``<B>+ </B>''.<DT><B>SHELL</B> <DD>This variable expands to the full pathname to the shell.If it is not set when the shell starts,<B>bash</B> assigns to it the full pathname of the current user's login shell.<DT><B>TIMEFORMAT</B> <DD>The value of this parameter is used as a format string specifyinghow the timing information for pipelines prefixed with the<B>time</B> reserved word should be displayed.The <B>%</B> character introduces an escape sequence that isexpanded to a time value or other information.The escape sequences and their meanings are as follows; thebraces denote optional portions.<P><DL COMPACT><DT><DD> <DL COMPACT><DT><B>%%</B> <DD>A literal <B>%</B>.<DT><B>%[</B><I>p</I>][l]R <DD>The elapsed time in seconds.<DT><B>%[</B><I>p</I>][l]U <DD>The number of CPU seconds spent in user mode.<DT><B>%[</B><I>p</I>][l]S <DD>The number of CPU seconds spent in system mode.<DT><B>%P</B> <DD>The CPU percentage, computed as (%U + %S) / %R. </DL></DL> <DT><DD>The optional <I>p</I> is a digit specifying the <I>precision</I>,the number of fractional digits after a decimal point.A value of 0 causes no decimal point or fraction to be output.At most three places after the decimal point may be specified;values of <I>p</I> greater than 3 are changed to 3.If <I>p</I> is not specified, the value 3 is used.<DT><DD>The optional <B>l</B> specifies a longer format, includingminutes, of the form <I>MM</I>m<I>SS</I>.<I>FF</I>s.The value of <I>p</I> determines whether or not the fraction isincluded.<DT><DD>If this variable is not set, <B>bash</B> acts as if it had thevalue <B>$aq\nreal\t%3lR\nuser\t%3lU\nsys\t%3lSaq</B>.If the value is null, no timing information is displayed.A trailing newline is added when the format string is displayed. <DT><B>TMOUT</B> <DD>If set to a value greater than zero,<FONT SIZE=-1><B>TMOUT</B> </FONT>is treated as thedefault timeout for the <B>read</B> builtin.The <B>select</B> command terminates if input does not arriveafter<FONT SIZE=-1><B>TMOUT</B> </FONT>seconds when input is coming from a terminal.In an interactive shell, the value is interpreted as thenumber of seconds to wait for a line of input after issuing theprimary prompt.<B>Bash</B> terminates after waiting for that number of seconds if a completeline of input does not arrive.<DT><B>TMPDIR</B> <DD>If set, <B>bash</B> uses its value as the name of a directory in which<B>bash</B> creates temporary files for the shell's use.<DT><B>auto_resume</B> <DD>This variable controls how the shell interacts with the user andjob control.  If this variable is set, single word simplecommands without redirections are treated as candidates for resumptionof an existing stopped job.  There is no ambiguity allowed; if there ismore than one job beginning with the string typed, the job most recentlyaccessed is selected.  The<I>name</I> of a stopped job, in this context, is the command line used tostart it.If set to the value<I>exact</I>, the string supplied must match the name of a stopped job exactly;if set to<I>substring</I>, the string supplied needs to match a substring of the name of astopped job.  The<I>substring</I> value provides functionality analogous to the<B>%?</B> job identifier (see<FONT SIZE=-1><B>JOB CONTROL</B> </FONT>below).  If set to any other value, the supplied string mustbe a prefix of a stopped job's name; this provides functionalityanalogous to the <B>%</B><I>string</I> job identifier.<DT><B>histchars</B> <DD>The two or three characters which control history expansionand tokenization (see<FONT SIZE=-1><B>HISTORY EXPANSION</B> </FONT>below).  The first character is the <I>history expansion</I> character,the character which signals the start of a historyexpansion, normally `<B>!</B>'.The second character is the <I>quick substitution</I>character, which is used as shorthand for re-running the previouscommand entered, substituting one string for another in the command.The default is `<B>^</B>'.The optional third character is the characterwhich indicates that the remainder of the line is a comment when foundas the first character of a word, normally `<B>#</B>'.  The historycomment character causes history substitution to be skipped for theremaining words on the line.  It does not necessarily cause the shellparser to treat the rest of the line as a comment. </DL><A NAME="lbAX">&nbsp;</A><H4>Arrays</H4> <B>Bash</B> provides one-dimensional indexed and associative array variables.Any variable may be used as an indexed array; the<B>declare</B> builtin will explicitly declare an array.There is no maximumlimit on the size of an array, nor any requirement that membersbe indexed or assigned contiguously.Indexed arrays are referenced using integers (including arithmeticexpressions) and are zero-based; associative arrays are referencedusing arbitrary strings.Unless otherwise noted, indexed array indices must be non-negative integers.<P> An indexed array is created automatically if any variable is assigned tousing the syntax <I>name</I>[<I>subscript</I>]=<I>value</I>.  The<I>subscript</I> is treated as an arithmetic expression that must evaluate to a number.To explicitly declare an indexed array, use<B>declare -a </B><I>name</I> (see<FONT SIZE=-1><B>SHELL BUILTIN COMMANDS</B> </FONT>below).<B>declare -a </B><I>name</I>[<I>subscript</I>] is also accepted; the <I>subscript</I> is ignored.<P> Associative arrays are created using<B>declare -A </B><I>name</I>. <P> Attributes may bespecified for an array variable using the<B>declare</B> and<B>readonly</B> builtins.  Each attribute applies to all members of an array.<P> Arrays are assigned to using compound assignments of the form<I>name</I>=<B>(</B>value<I>1</I> ... value<I>n</I><B>)</B>, where each<I>value</I> may be of the form [<I>subscript</I>]=<I>string</I>.Indexed array assignments do not require anything but <I>string</I>.Each <I>value</I> in the list is expanded using all the shell expansionsdescribed below under<FONT SIZE=-1><B>EXPANSION</B>. </FONT>When assigning to indexed arrays, if the optional brackets and subscriptare supplied, that index is assigned to;otherwise the index of the element assigned is the last index assignedto by the statement plus one.  Indexing starts at zero.<P> When assigning to an associative array, the words in a compound assignmentmay be either assignment statements, for which the subscript is required,or a list of words that is interpreted as a sequence of alternating keysand values:<I>name</I>=<B>( </B><I>key1 value1 key2 value2</I> ...<B>)</B>.These are treated identically to<I>name</I>=<B>(</B> [<I>key1</I>]=<I>value1</I> [<I>key2</I>]=<I>value2</I> ...<B>)</B>.The first word in the list determines how the remaining wordsare interpreted; all assignments in a list must be of the same type.When using key/value pairs, the keys may not be missing or empty;a final missing value is treated like the empty string.<P> This syntax is also accepted by the<B>declare</B> builtin.  Individual array elements may be assigned to using the<I>name</I>[<I>subscript</I>]=<I>value</I> syntax introduced above.When assigning to an indexed array, if<I>name</I> is subscripted by a negative number, that number isinterpreted as relative to one greater than the maximum index of<I>name</I>, so negative indices count back from the end of thearray, and an index of -1 references the last element.<P> The += operator will append to an array variable when assigningusing the compound assignment syntax; see<FONT SIZE=-1><B>PARAMETERS</B> </FONT>above.<P> Any element of an array may be referenced using${<I>name</I>[<I>subscript</I>]}.  The braces are required to avoidconflicts with pathname expansion.  If<I>subscript</I> is <B>@</B> or <B>*</B>, the word expands toall members of <I>name</I>.  These subscripts differ only when theword appears within double quotes.  If the word is double-quoted,${<I>name</I>[*]} expands to a singleword with the value of each array member separated by the firstcharacter of the<FONT SIZE=-1><B>IFS</B> </FONT>special variable, and ${<I>name</I>[@]} expands each element of<I>name</I> to a separate word.  When there are no array members,${<I>name</I>[@]} expands to nothing.If the double-quoted expansion occurs within a word, the expansion ofthe first parameter is joined with the beginning part of the originalword, and the expansion of the last parameter is joined with the lastpart of the original word.This is analogous to the expansionof the special parameters <B>*</B> and <B>@</B> (see<B>Special Parameters</B> above).  ${#<I>name</I>[<I>subscript</I>]} expands to the length of${<I>name</I>[<I>subscript</I>]}.  If <I>subscript</I> is <B>*</B> or<B>@</B>, the expansion is the number of elements in the array.If the<I>subscript</I> used to reference an element of an indexed arrayevaluates to a number less than zero, it isinterpreted as relative to one greater than the maximum index of the array,so negative indices count back from the end of thearray, and an index of -1 references the last element.<P> Referencing an array variable without a subscript is equivalent toreferencing the array with a subscript of 0.Any reference to a variable using a valid subscript is legal, and<B>bash</B> will create an array if necessary.<P> An array variable is considered set if a subscript has been assigned avalue.  The null string is a valid value.<P> It is possible to obtain the keys (indices) of an array as well as the values.${<B>!</B><I>name</I>[<I>@</I>]} and ${<B>!</B><I>name</I>[<I>*</I>]}expand to the indices assigned in array variable <I>name</I>.The treatment when in double quotes is similar to the expansion of thespecial parameters <I>@</I> and <I>*</I> within double quotes.<P> The<B>unset</B> builtin is used to destroy arrays.  <B>unset</B> <I>name</I>[<I>subscript</I>]destroys the array element at index <I>subscript</I>,for both indexed and associative arrays.Negative subscripts to indexed arrays are interpreted as described above.Unsetting the last element of an array variable does not unset the variable.<B>unset</B> <I>name</I>, where <I>name</I> is an array,removes the entire array.<B>unset</B> <I>name</I>[<I>subscript</I>], where<I>subscript</I> is <B>*</B> or <B>@</B>, behaves differently depending onwhether <I>name</I> is an indexed or associative array.If <I>name</I> is an associative array, this unsets the element withsubscript <B>*</B> or <B>@</B>.If <I>name</I> is an indexed array, unset removes all of the elements butdoes not remove the array itself.<P> When using a variable name with a subscript as an argument to a command,such as with <B>unset</B>, without using the word expansion syntaxdescribed above, the argument is subject to pathname expansion.If pathname expansion is not desired, the argument should be quoted.<P> The<B>declare</B>, <B>local</B>, and<B>readonly</B> builtins each accept a<B>-a</B> option to specify an indexed array and a<B>-A</B> option to specify an associative array.If both options are supplied,<B>-A</B> takes precedence.The<B>read</B> builtin accepts a<B>-a</B> option to assign a list of words read from the standard inputto an array.  The<B>set</B> and<B>declare</B> builtins display array values in a way that allows them to bereused as assignments.<A NAME="lbAY">&nbsp;</A><H3>EXPANSION</H3> Expansion is performed on the command line after it has been split intowords.  There are seven kinds of expansion performed:<I>brace expansion</I>, <I>tilde expansion</I>, <I>parameter and variable expansion</I>, <I>command substitution</I>, <I>arithmetic expansion</I>, <I>word splitting</I>, and<I>pathname expansion</I>. <P> The order of expansions is:brace expansion;tilde expansion, parameter and variable expansion, arithmetic expansion,and command substitution (done in a left-to-right fashion);word splitting;and pathname expansion.<P> On systems that can support it, there is an additional expansionavailable: <I>process substitution</I>.This is performed at thesame time as tilde, parameter, variable, and arithmetic expansion andcommand substitution.<P> After these expansions are performed, quote characters present in theoriginal word are removed unless they have been quoted themselves(<I>quote removal</I>).<P> Only brace expansion, word splitting, and pathname expansioncan increase the number of words of the expansion; other expansionsexpand a single word to a single word.The only exceptions to this are the expansions of&quot;<B>$@</B>&quot; and &quot;<B>${</B><I>name</I><B>[@]}</B>&quot;,and, in most cases, <B>$*</B> and <B>${</B><I>name</I><B>[*]}</B>as explained above (see<FONT SIZE=-1><B>PARAMETERS</B>). </FONT><A NAME="lbAZ">&nbsp;</A><H4>Brace Expansion</H4> <I>Brace expansion</I> is a mechanism by which arbitrary stringsmay be generated.  This mechanism is similar to<I>pathname expansion</I>, but the filenames generatedneed not exist.  Patterns to be brace expanded takethe form of an optional<I>preamble</I>, followed by either a series of comma-separated strings ora sequence expression between a pair of braces, followed byan optional<I>postscript</I>. The preamble is prefixed to each string containedwithin the braces, and the postscript is then appendedto each resulting string, expanding left to right.<P> Brace expansions may be nested.  The results of each expandedstring are not sorted; left to right order is preserved.For example, a<B>{</B>d,c,b<B>}</B>e expands into `ade ace abe'.<P> A sequence expression takes the form<B>{</B><I>x</I><B>..</B><I>y</I><B>[..</B><I>incr</I><B>]}</B>,where <I>x</I> and <I>y</I> are either integers or single letters,and <I>incr</I>, an optional increment, is an integer.When integers are supplied, the expression expands to each number between<I>x</I> and <I>y</I>, inclusive.Supplied integers may be prefixed with <I>0</I> to force each term to have thesame width.When either <I>x</I> or y begins with a zero, the shellattempts to force all generated terms to contain the same number of digits,zero-padding where necessary.When letters are supplied, the expression expands to each characterlexicographically between <I>x</I> and <I>y</I>, inclusive,using the default C locale.Note that both <I>x</I> and <I>y</I> must be of the same type(integer or letter).When the increment is supplied, it is used as the difference betweeneach term.  The default increment is 1 or -1 as appropriate.<P> Brace expansion is performed before any other expansions,and any characters special to other expansions are preservedin the result.  It is strictly textual.<B>Bash</B> does not apply any syntactic interpretation to the context of theexpansion or the text between the braces.<P> A correctly-formed brace expansion must contain unquoted openingand closing braces, and at least one unquoted comma or a validsequence expression.Any incorrectly formed brace expansion is left unchanged.A <B>{</B> or <B>,</B> may be quoted with a backslash to prevent itsbeing considered part of a brace expression.To avoid conflicts with parameter expansion, the string <B>${</B>is not considered eligible for brace expansion, and inhibits braceexpansion until the closing <B>}</B>.<P> This construct is typically used as shorthand when the commonprefix of the strings to be generated is longer than in theabove example:<DL COMPACT><DT><DD><P> mkdir /usr/local/src/bash/{old,new,dist,bugs}</DL> or<DL COMPACT><DT><DD>chown root /usr/{ucb/{ex,edit},lib/{ex?.?*,how_ex}}</DL> <P> Brace expansion introduces a slight incompatibility withhistorical versions of<B>sh</B>. <B>sh</B> does not treat opening or closing braces specially when theyappear as part of a word, and preserves them in the output.<B>Bash</B> removes braces from words as a consequence of braceexpansion.  For example, a word entered to<B>sh</B> as <I>file{1,2}</I>appears identically in the output.  The same word isoutput as<I>file1 file2</I> after expansion by<B>bash</B>. If strict compatibility with<B>sh</B> is desired, start<B>bash</B> with the<B>+B</B> option or disable brace expansion with the<B>+B</B> option to the<B>set</B> command (see<FONT SIZE=-1><B>SHELL BUILTIN COMMANDS</B> </FONT>below).<A NAME="lbBA">&nbsp;</A><H4>Tilde Expansion</H4> If a word begins with an unquoted tilde character (`<B>~</B>'), all ofthe characters preceding the first unquoted slash (or all characters,if there is no unquoted slash) are considered a <I>tilde-prefix</I>.If none of the characters in the tilde-prefix are quoted, thecharacters in the tilde-prefix following the tilde are treated as apossible <I>login name</I>.If this login name is the null string, the tilde is replaced with thevalue of the shell parameter<FONT SIZE=-1><B>HOME</B>. </FONT>If<FONT SIZE=-1><B>HOME</B> </FONT>is unset, the home directory of the user executing the shell issubstituted instead.Otherwise, the tilde-prefix is replaced with the home directoryassociated with the specified login name.<P> If the tilde-prefix is a `~+', the value of the shell variable<FONT SIZE=-1><B>PWD</B> </FONT>replaces the tilde-prefix.If the tilde-prefix is a `~-', the value of the shell variable<FONT SIZE=-1><B>OLDPWD</B>, </FONT>if it is set, is substituted.If the characters following the tilde in the tilde-prefix consistof a number <I>N</I>, optionally prefixedby a `+' or a `-', the tilde-prefix is replaced with the correspondingelement from the directory stack, as it would be displayed by the<B>dirs</B> builtin invoked with the tilde-prefix as an argument.If the characters following the tilde in the tilde-prefix consist of anumber without a leading `+' or `-', `+' is assumed.<P> If the login name is invalid, or the tilde expansion fails, the wordis unchanged.<P> Each variable assignment is checked for unquoted tilde-prefixes immediatelyfollowing a<B>:</B> or the first<B>=</B>. In these cases, tilde expansion is also performed.Consequently, one may use filenames with tildes in assignments to<FONT SIZE=-1><B>PATH</B>, </FONT><FONT SIZE=-1><B>MAILPATH</B>, </FONT>and<FONT SIZE=-1><B>CDPATH</B>, </FONT>and the shell assigns the expanded value.<P> Bash also performs tilde expansion on words satisfying the conditions ofvariable assignments (as described above under<FONT SIZE=-1><B>PARAMETERS</B>) </FONT>when they appear as arguments to simple commands.Bash does not do this, except for the <I>declaration</I> commands listedabove, when in <I>posix mode</I>.<A NAME="lbBB">&nbsp;</A><H4>Parameter Expansion</H4> The `<B>$</B>' character introduces parameter expansion,command substitution, or arithmetic expansion.  The parameter nameor symbol to be expanded may be enclosed in braces, whichare optional but serve to protect the variable to be expanded fromcharacters immediately following it which could beinterpreted as part of the name.<P> When braces are used, the matching ending brace is the first `<B>}</B>'not escaped by a backslash or within a quoted string, and not within anembedded arithmetic expansion, command substitution, or parameterexpansion.<P>  <DL COMPACT><DT>${<I>parameter</I>}<DD>The value of <I>parameter</I> is substituted.  The braces are requiredwhen<I>parameter</I> is a positional parameter with more than one digit,or when<I>parameter</I> is followed by a character which is not to beinterpreted as part of its name.The <I>parameter</I> is a shell parameter as described above<B>PARAMETERS</B>) or an array reference (<B>Arrays</B>). </DL><P> If the first character of <I>parameter</I> is an exclamation point (<B>!</B>),and <I>parameter</I> is not a <I>nameref</I>,it introduces a level of indirection.<B>Bash</B> uses the value formed by expanding the rest of<I>parameter</I> as the new <I>parameter</I>; this is thenexpanded and that value is used in the rest of the expansion, ratherthan the expansion of the original <I>parameter</I>.This is known as <I>indirect expansion</I>.The value is subject to tilde expansion,parameter expansion, command substitution, and arithmetic expansion.If <I>parameter</I> is a nameref, this expands to the name of theparameter referenced by <I>parameter</I> instead of performing thecomplete indirect expansion.The exceptions to this are the expansions of ${<B>!</B><I>prefix</I><B>*</B>} and${<B>!</B><I>name</I>[<I>@</I>]} described below.The exclamation point must immediately follow the left brace in order tointroduce indirection.<P> In each of the cases below, <I>word</I> is subject to tilde expansion,parameter expansion, command substitution, and arithmetic expansion.<P> When not performing substring expansion, using the forms documented below(e.g., <B>:-</B>),<B>bash</B> tests for a parameter that is unset or null.  Omitting the colonresults in a test only for a parameter that is unset.<P>  <DL COMPACT><DT>${<I>parameter</I><B>:-</B><I>word</I>}<DD><B>Use Default Values</B>.  If<I>parameter</I> is unset or null, the expansion of<I>word</I> is substituted.  Otherwise, the value of<I>parameter</I> is substituted.<DT>${<I>parameter</I><B>:=</B><I>word</I>}<DD><B>Assign Default Values</B>.If<I>parameter</I> is unset or null, the expansion of<I>word</I> is assigned to<I>parameter</I>. The value of<I>parameter</I> is then substituted.  Positional parameters and special parameters maynot be assigned to in this way.<DT>${<I>parameter</I><B>:?</B><I>word</I>}<DD><B>Display Error if Null or Unset</B>.If<I>parameter</I> is null or unset, the expansion of <I>word</I> (or a message to that effectif<I>word</I> is not present) is written to the standard error and the shell, if itis not interactive, exits.  Otherwise, the value of <I>parameter</I> issubstituted.<DT>${<I>parameter</I><B>:+</B><I>word</I>}<DD><B>Use Alternate Value</B>.If<I>parameter</I> is null or unset, nothing is substituted, otherwise the expansion of<I>word</I> is substituted.<DT>${<I>parameter</I><B>:</B><I>offset</I>}<DD> <DT>${<I>parameter</I><B>:</B><I>offset</I><B>:</B><I>length</I>}<DD> <B>Substring Expansion</B>.Expands to up to <I>length</I> characters of the value of <I>parameter</I>starting at the character specified by <I>offset</I>.If <I>parameter</I> is <B>@</B> or <B>*</B>, an indexed array subscripted by<B>@</B> or <B>*</B>, or an associative array name, the results differ asdescribed below.If <I>length</I> is omitted, expands to the substring of the value of<I>parameter</I> starting at the character specified by <I>offset</I>and extending to the end of the value.<I>length</I> and <I>offset</I> are arithmetic expressions (see<FONT SIZE=-1><B>ARITHMETIC EVALUATION</B> </FONT>below).<P>If <I>offset</I> evaluates to a number less than zero, the valueis used as an offset in charactersfrom the end of the value of <I>parameter</I>.If <I>length</I> evaluates to a number less than zero,it is interpreted as an offset in charactersfrom the end of the value of <I>parameter</I> rather thana number of characters, and the expansion is the characters between<I>offset</I> and that result.Note that a negative offset must be separated from the colon by at leastone space to avoid being confused with the <B>:-</B> expansion.<P>If <I>parameter</I> is <B>@</B> or <B>*</B>, the result is <I>length</I>positional parameters beginning at <I>offset</I>.A negative <I>offset</I> is taken relative to one greater than the greatestpositional parameter, so an offset of -1 evaluates to the last positionalparameter.It is an expansion error if <I>length</I> evaluates to a number less thanzero.<P>If <I>parameter</I> is an indexed array name subscripted by @ or *,the result is the <I>length</I>members of the array beginning with ${<I>parameter</I>[<I>offset</I>]}.A negative <I>offset</I> is taken relative to one greater than the maximumindex of the specified array.It is an expansion error if <I>length</I> evaluates to a number less thanzero.<P>Substring expansion applied to an associative array produces undefinedresults.<P>Substring indexing is zero-based unless the positional parametersare used, in which case the indexing starts at 1 by default.If <I>offset</I> is 0, and the positional parameters are used, <B>$0</B> isprefixed to the list.<DT>${<B>!</B><I>prefix</I><B>*</B>}<DD> <DT>${<B>!</B><I>prefix</I><B>@</B>}<DD> <B>Names matching prefix</B>.Expands to the names of variables whose names begin with <I>prefix</I>,separated by the first character of the<FONT SIZE=-1><B>IFS</B> </FONT>special variable.When <I>@</I> is used and the expansion appears within double quotes, eachvariable name expands to a separate word.<DT>${<B>!</B><I>name</I>[<I>@</I>]}<DD> <DT>${<B>!</B><I>name</I>[<I>*</I>]}<DD> <B>List of array keys</B>.If <I>name</I> is an array variable, expands to the list of array indices(keys) assigned in <I>name</I>.If <I>name</I> is not an array, expands to 0 if <I>name</I> is set and nullotherwise.When <I>@</I> is used and the expansion appears within double quotes, eachkey expands to a separate word.<DT>${<B>#</B><I>parameter</I>}<DD><B>Parameter length</B>.The length in characters of the value of <I>parameter</I> is substituted.If<I>parameter</I> is<B>*</B> or<B>@</B>, the value substituted is the number of positional parameters.If<I>parameter</I> is an array name subscripted by<B>*</B> or<B>@</B>, the value substituted is the number of elements in the array.If<I>parameter</I> is an indexed array name subscripted by a negative number, that number isinterpreted as relative to one greater than the maximum index of<I>parameter</I>, so negative indices count back from the end of thearray, and an index of -1 references the last element.<DT>${<I>parameter</I><B>#</B><I>word</I>}<DD> <DT>${<I>parameter</I><B>##</B><I>word</I>}<DD> <B>Remove matching prefix pattern</B>.The<I>word</I> is expanded to produce a pattern just as in pathnameexpansion, and matched against the expanded value of<I>parameter</I> using the rules described under<B>Pattern Matching</B> below.If the pattern matches the beginning ofthe value of<I>parameter</I>, then the result of the expansion is the expanded value of<I>parameter</I> with the shortest matching pattern (the ``<B>#</B>'' case) or thelongest matching pattern (the ``<B>##</B>'' case) deleted.If<I>parameter</I> is<B>@</B> or<B>*</B>, the pattern removal operation is applied to each positionalparameter in turn, and the expansion is the resultant list.If<I>parameter</I> is an array variable subscripted with<B>@</B> or<B>*</B>, the pattern removal operation is applied to each member of thearray in turn, and the expansion is the resultant list.<DT>${<I>parameter</I><B>%</B><I>word</I>}<DD> <DT>${<I>parameter</I><B>%%</B><I>word</I>}<DD> <B>Remove matching suffix pattern</B>.The <I>word</I> is expanded to produce a pattern just as inpathname expansion, and matched against the expanded value of<I>parameter</I> using the rules described under<B>Pattern Matching</B> below.If the pattern matches a trailing portion of the expanded value of<I>parameter</I>, then the result of the expansion is the expanded value of<I>parameter</I> with the shortest matching pattern (the ``<B>%</B>'' case) or thelongest matching pattern (the ``<B>%%</B>'' case) deleted.If<I>parameter</I> is<B>@</B> or<B>*</B>, the pattern removal operation is applied to each positionalparameter in turn, and the expansion is the resultant list.If<I>parameter</I> is an array variable subscripted with<B>@</B> or<B>*</B>, the pattern removal operation is applied to each member of thearray in turn, and the expansion is the resultant list.<DT>${<I>parameter</I><B>/</B><I>pattern</I><B>/</B><I>string</I>}<DD> <DT>${<I>parameter</I><B>//</B><I>pattern</I><B>/</B><I>string</I>}<DD><DT>${<I>parameter</I><B>/#</B><I>pattern</I><B>/</B><I>string</I>}<DD><DT>${<I>parameter</I><B>/%</B><I>pattern</I><B>/</B><I>string</I>}<DD> <B>Pattern substitution</B>.The <I>pattern</I> is expanded to produce a pattern just as inpathname expansion.<I>Parameter</I> is expanded and the longest match of <I>pattern</I>against its value is replaced with <I>string</I>.<I>string</I> undergoes tilde expansion, parameter and variable expansion,arithmetic expansion, command and process substitution, and quote removal.The match is performed using the rules described under<B>Pattern Matching</B> below.In the first form above, only the first match is replaced.If there are two slashes separating <I>parameter</I> and <I>pattern</I> (the second form above), all matches of <I>pattern</I> arereplaced with <I>string</I>.If <I>pattern</I> is preceded by <B>#</B> (the third form above),it must match at the beginning of the expanded value of <I>parameter</I>.If <I>pattern</I> is preceded by <B>%</B> (the fourth form above),it must match at the end of the expanded value of <I>parameter</I>.If the expansion of <I>string</I> is null,matches of <I>pattern</I> are deleted.If <I>string</I> is null,matches of <I>pattern</I> are deletedand the <B>/</B> following <I>pattern</I> may be omitted.<P>If the <B>patsub_replacement</B> shell option is enabled using <B>shopt</B>,any unquoted instances of <B>&amp;</B> in <I>string</I> are replaced with thematching portion of <I>pattern</I>.<P>Quoting any part of <I>string</I> inhibits replacement in theexpansion of the quoted portion, including replacement strings storedin shell variables.Backslash will escape <B>&amp;</B> in <I>string</I>; the backslash is removedin order to permit a literal <B>&amp;</B> in the replacement string.Backslash can also be used to escape a backslash; <B>\\</B> results ina literal backslash in the replacement.Users should take care if <I>string</I> is double-quoted to avoidunwanted interactions between the backslash and double-quoting, sincebackslash has special meaning within double quotes.Pattern substitution performs the check for unquoted <B>&amp;</B> afterexpanding <I>string</I>;shell programmers should quote any occurrences of <B>&amp;</B>they want to be taken literally in the replacementand ensure any instances of <B>&amp;</B> they want to be replaced are unquoted.<P>If the<B>nocasematch</B> shell option is enabled, the match is performed without regard to the caseof alphabetic characters.If<I>parameter</I> is<B>@</B> or<B>*</B>, the substitution operation is applied to each positionalparameter in turn, and the expansion is the resultant list.If<I>parameter</I> is an array variable subscripted with<B>@</B> or<B>*</B>, the substitution operation is applied to each member of thearray in turn, and the expansion is the resultant list.<DT>${<I>parameter</I><B>^</B><I>pattern</I>}<DD> <DT>${<I>parameter</I><B>^^</B><I>pattern</I>}<DD><DT>${<I>parameter</I><B>,</B><I>pattern</I>}<DD><DT>${<I>parameter</I><B>,,</B><I>pattern</I>}<DD> <B>Case modification</B>.This expansion modifies the case of alphabetic characters in <I>parameter</I>.The <I>pattern</I> is expanded to produce a pattern just as inpathname expansion.Each character in the expanded value of <I>parameter</I> is tested against<I>pattern</I>, and, if it matches the pattern, its case is converted.The pattern should not attempt to match more than one character.The <B>^</B> operator converts lowercase letters matching <I>pattern</I>to uppercase; the <B>,</B> operator converts matching uppercase lettersto lowercase.The <B>^^</B> and <B>,,</B> expansions convert each matched character in theexpanded value; the <B>^</B> and <B>,</B> expansions match and convert onlythe first character in the expanded value.If <I>pattern</I> is omitted, it is treated like a <B>?</B>, which matchesevery character.If<I>parameter</I> is<B>@</B> or<B>*</B>, the case modification operation is applied to each positionalparameter in turn, and the expansion is the resultant list.If<I>parameter</I> is an array variable subscripted with<B>@</B> or<B>*</B>, the case modification operation is applied to each member of thearray in turn, and the expansion is the resultant list.<DT>${<I>parameter</I><B>@</B><I>operator</I>}<DD><B>Parameter transformation</B>.The expansion is either a transformation of the value of <I>parameter</I>or information about <I>parameter</I> itself, depending on the value of<I>operator</I>.  Each <I>operator</I> is a single letter:<P><DL COMPACT><DT><DD> <DL COMPACT><DT><B>U</B> <DD>The expansion is a string that is the value of <I>parameter</I> with lowercasealphabetic characters converted to uppercase.<DT><B>u</B> <DD>The expansion is a string that is the value of <I>parameter</I> with the firstcharacter converted to uppercase, if it is alphabetic.<DT><B>L</B> <DD>The expansion is a string that is the value of <I>parameter</I> with uppercasealphabetic characters converted to lowercase.<DT><B>Q</B> <DD>The expansion is a string that is the value of <I>parameter</I> quoted in aformat that can be reused as input.<DT><B>E</B> <DD>The expansion is a string that is the value of <I>parameter</I> with backslashescape sequences expanded as with the <B>$aq...aq</B> quoting mechanism.<DT><B>P</B> <DD>The expansion is a string that is the result of expanding the value of<I>parameter</I> as if it were a prompt string (see <B>PROMPTING</B> below).<DT><B>A</B> <DD>The expansion is a string in the form ofan assignment statement or <B>declare</B> command that, ifevaluated, will recreate <I>parameter</I> with its attributes and value.<DT><B>K</B> <DD>Produces a possibly-quoted version of the value of <I>parameter</I>,except that it prints the values ofindexed and associative arrays as a sequence of quoted key-value pairs(see <B>Arrays</B> above).<DT><B>a</B> <DD>The expansion is a string consisting of flag values representing<I>parameter</I>'s attributes.<DT><B>k</B> <DD>Like the K transformation, but expands the keys and values ofindexed and associative arrays to separate words after word splitting. </DL><P> If<I>parameter</I> is<B>@</B> or<B>*</B>, the operation is applied to each positionalparameter in turn, and the expansion is the resultant list.If<I>parameter</I> is an array variable subscripted with<B>@</B> or<B>*</B>, the operation is applied to each member of thearray in turn, and the expansion is the resultant list.<P>The result of the expansion is subject to word splitting and pathnameexpansion as described below.</DL> </DL><A NAME="lbBC">&nbsp;</A><H4>Command Substitution</H4> <I>Command substitution</I> allows the output of a command to replacethe command name.  There are two forms:<DL COMPACT><DT><DD><P> <B>$(</B><I>command</I><B>)</B></DL> or<DL COMPACT><DT><DD><B>`</B><I>command</I><B>`</B></DL> <P> <B>Bash</B> performs the expansion by executing <I>command</I> in a subshell environmentand replacing the command substitution with the standard output of thecommand, with any trailing newlines deleted.Embedded newlines are not deleted, but they may be removed duringword splitting.The command substitution <B>$(cat </B><I>file</I>) can be replaced bythe equivalent but faster <B>$(&lt; </B><I>file</I>).<P> When the old-style backquote form of substitution is used,backslash retains its literal meaning except when followed by<B>$</B>, <B>`</B>, or<B>\</B>. The first backquote not preceded by a backslash terminates thecommand substitution.When using the $(<I>command</I>) form, all characters between theparentheses make up the command; none are treated specially.<P> Command substitutions may be nested.  To nest when using the backquoted form,escape the inner backquotes with backslashes.<P> If the substitution appears within double quotes, word splitting andpathname expansion are not performed on the results.<A NAME="lbBD">&nbsp;</A><H4>Arithmetic Expansion</H4> Arithmetic expansion allows the evaluation of an arithmetic expressionand the substitution of the result.  The format for arithmetic expansion is:<DL COMPACT><DT><DD><P> <B>$((</B><I>expression</I><B>))</B></DL> <P> The<I>expression</I> undergoes the same expansionsas if it were within double quotes,but double quote characters in <I>expression</I> are not treated speciallyand are removed.All tokens in the expression undergo parameter and variable expansion,command substitution, and quote removal.The result is treated as the arithmetic expression to be evaluated.Arithmetic expansions may be nested.<P> The evaluation is performed according to the rules listed below under<FONT SIZE=-1><B>ARITHMETIC EVALUATION</B>. </FONT>If<I>expression</I> is invalid,<B>bash</B> prints a message indicating failure and no substitution occurs.<A NAME="lbBE">&nbsp;</A><H4>Process Substitution</H4> <I>Process substitution</I> allows a process's input or output to bereferred to using a filename.It takes the form of<B>&lt;(</B><I>list</I><B>)</B>or<B>&gt;(</B><I>list</I><B>)</B>.The process <I>list</I> is run asynchronously, and its input or outputappears as a filename.This filename ispassed as an argument to the current command as the result of theexpansion.If the <B>&gt;(</B><I>list</I><B>)</B> form is used, writing tothe file will provide input for <I>list</I>.  If the<B>&lt;(</B><I>list</I><B>)</B> form is used, the file passed as anargument should be read to obtain the output of <I>list</I>.Process substitution is supported on systems that support namedpipes (<I>FIFOs</I>) or the <B>/dev/fd</B> method of naming open files.<P> When available, process substitution is performedsimultaneously with parameter and variable expansion,command substitution,and arithmetic expansion.<A NAME="lbBF">&nbsp;</A><H4>Word Splitting</H4> The shell scans the results ofparameter expansion,command substitution,andarithmetic expansionthat did not occur within double quotes for<I>word splitting</I>. <P> The shell treats each character of<FONT SIZE=-1><B>IFS</B> </FONT>as a delimiter, and splits the results of the otherexpansions into words using these characters as field terminators.If<FONT SIZE=-1><B>IFS</B> </FONT>is unset, or itsvalue is exactly<B>&lt;space&gt;&lt;tab&gt;&lt;newline&gt;</B>, the default, thensequences of<B>&lt;space&gt;</B>, <B>&lt;tab&gt;</B>, and<B>&lt;newline&gt;</B> at the beginning and end of the results of the previousexpansions are ignored, andany sequence of<FONT SIZE=-1><B>IFS</B> </FONT>characters not at the beginning or end serves to delimit words.If<FONT SIZE=-1><B>IFS</B> </FONT>has a value other than the default, then sequences ofthe whitespace characters<B>space</B>, <B>tab</B>, and<B>newline</B> are ignored at the beginning and end of theword, as long as the whitespace character is in thevalue of<FONT SIZE=-1><B>IFS</B> </FONT>(an<FONT SIZE=-1><B>IFS</B> </FONT>whitespace character).Any character in<FONT SIZE=-1><B>IFS</B> </FONT>that is not<FONT SIZE=-1><B>IFS</B> </FONT>whitespace, along with any adjacent<FONT SIZE=-1><B>IFS</B> </FONT>whitespace characters, delimits a field.A sequence of<FONT SIZE=-1><B>IFS</B> </FONT>whitespace characters is also treated as a delimiter.If the value of<FONT SIZE=-1><B>IFS</B> </FONT>is null, no word splitting occurs.<P> Explicit null arguments (<B>&quot;&quot;</B> or <B>aqaq</B>) are retainedand passed to commands as empty strings.Unquoted implicit null arguments, resulting from the expansion ofparameters that have no values, are removed.If a parameter with no value is expanded within double quotes, anull argument results and is retainedand passed to a command as an empty string.When a quoted null argument appears as part of a word whose expansion isnon-null, the null argument is removed.That is, the word<TT>-daqaq</TT> becomes <TT>-d</TT> after word splitting andnull argument removal.<P> Note that if no expansion occurs, no splittingis performed.<A NAME="lbBG">&nbsp;</A><H4>Pathname Expansion</H4> After word splitting,unless the<B>-f</B> option has been set,<B>bash</B> scans each word for the characters<B>*</B>, <B>?</B>, and<B>[</B>. If one of these characters appears, and is not quoted, then the word isregarded as a<I>pattern</I>, and replaced with an alphabetically sorted list offilenames matching the pattern(see<FONT SIZE=-1><B>Pattern Matching</B> </FONT>below).If no matching filenames are found,and the shell option<B>nullglob</B> is not enabled, the word is left unchanged.If the<B>nullglob</B> option is set, and no matches are found,the word is removed.If the<B>failglob</B> shell option is set, and no matches are found, an error messageis printed and the command is not executed.If the shell option<B>nocaseglob</B> is enabled, the match is performed without regard to the caseof alphabetic characters.When a pattern is used for pathname expansion,the character<B>``.''</B> at the start of a name or immediately following a slashmust be matched explicitly, unless the shell option<B>dotglob</B> is set.In order to match the filenames<B>``.''</B> and<B>``..''</B>, the pattern must begin with ``.'' (for example, ``.?''),even if<B>dotglob</B> is set.If the<B>globskipdots</B> shell option is enabled, the filenames<B>``.''</B> and<B>``..''</B> are never matched, even if the pattern begins with a<B>``.''</B>. When not matching pathnames, the<B>``.''</B> character is not treated specially.When matching a pathname, the slash character must always bematched explicitly by a slash in the pattern, but in other matchingcontexts it can be matched by a special pattern character as describedbelow under<FONT SIZE=-1><B>Pattern Matching</B>. </FONT>See the description of<B>shopt</B> below under<FONT SIZE=-1><B>SHELL BUILTIN COMMANDS</B> </FONT>for a description of the<B>nocaseglob</B>, <B>nullglob</B>, <B>globskipdots</B>, <B>failglob</B>, and<B>dotglob</B> shell options.<P> The<FONT SIZE=-1><B>GLOBIGNORE</B> </FONT>shell variable may be used to restrict the set of file names matching a<I>pattern</I>. If<FONT SIZE=-1><B>GLOBIGNORE</B> </FONT>is set, each matching file name that also matches one of the patterns in<FONT SIZE=-1><B>GLOBIGNORE</B> </FONT>is removed from the list of matches.If the <B>nocaseglob</B> option is set, the matching against the patterns in<FONT SIZE=-1><B>GLOBIGNORE</B> </FONT>is performed without regard to case.The filenames<B>``.''</B> and<B>``..''</B> are always ignored when<FONT SIZE=-1><B>GLOBIGNORE</B> </FONT>is set and not null.  However, setting<FONT SIZE=-1><B>GLOBIGNORE</B> </FONT>to a non-null value has the effect of enabling the<B>dotglob</B> shell option, so all other filenames beginning with a<B>``.''</B> will match.To get the old behavior of ignoring filenames beginning with a<B>``.''</B>, make<B>``.*''</B> one of the patterns in<FONT SIZE=-1><B>GLOBIGNORE</B>. </FONT>The<B>dotglob</B> option is disabled when<FONT SIZE=-1><B>GLOBIGNORE</B> </FONT>is unset.The pattern matching honors the setting of the <B>extglob</B> shelloption.<P> <B>Pattern Matching</B><P> Any character that appears in a pattern, other than the special patterncharacters described below, matches itself.  The NUL character may notoccur in a pattern.  A backslash escapes the following character; theescaping backslash is discarded when matching.The special pattern characters must be quoted ifthey are to be matched literally.<P> The special pattern characters have the following meanings:<P>  <DL COMPACT><DT><DD><DL COMPACT><DT><B>*</B> <DD>Matches any string, including the null string.When the <B>globstar</B> shell option is enabled, and <B>*</B> is used ina pathname expansion context, two adjacent <B>*</B>s used as a singlepattern will match all files and zero or more directories andsubdirectories.If followed by a <B>/</B>, two adjacent <B>*</B>s will match only directoriesand subdirectories.<DT><B>?</B> <DD>Matches any single character.<DT><B>[...]</B> <DD>Matches any one of the enclosed characters.  A pair of charactersseparated by a hyphen denotes a<I>range expression</I>;any character that falls between those two characters, inclusive,using the current locale's collating sequence and character set,is matched.  If the first character following the<B>[</B> is a<B>!</B> or a<B>^</B> then any character not enclosed is matched.The sorting order of characters in range expressions,and the characters included in the range,are determined bythe current locale and the values of the<FONT SIZE=-1><B>LC_COLLATE</B> </FONT>or<FONT SIZE=-1><B>LC_ALL</B> </FONT>shell variables, if set.To obtain the traditional interpretation of range expressions, where<B>[a-d]</B> is equivalent to<B>[abcd]</B>, set value of the<B>LC_ALL</B> shell variable to<B>C</B>, or enable the<B>globasciiranges</B> shell option.A<B>-</B> may be matched by including it as the first or last characterin the set.A<B>]</B> may be matched by including it as the first characterin the set.<BR> <P>  Within<B>[</B> and<B>]</B>, <I>character classes</I> can be specified using the syntax<B>[:</B><I>class</I><B>:]</B>, where <I>class</I> is one of thefollowing classes defined in the POSIX standard:</DL><P> <DL COMPACT><DT><DD><B></B> alnum   alpha   ascii   blank   cntrl   digit   graph   lower   print   punct   space   upper   word   xdigit<BR> A character class matches any character belonging to that class.The <B>word</B> character class matches letters, digits, and the character _.<BR> <P>  Within<B>[</B> and<B>]</B>, an <I>equivalence class</I> can be specified using the syntax<B>[=</B><I>c</I><B>=]</B>, which matches all characters with thesame collation weight (as defined by the current locale) asthe character <I>c</I>.<BR> <P>  Within<B>[</B> and<B>]</B>, the syntax <B>[.</B><I>symbol</I><B>.]</B> matches the collating symbol<I>symbol</I>.</DL> </DL>  <P> If the <B>extglob</B> shell option is enabled using the <B>shopt</B>builtin, the shell recognizes several extended pattern matching operators.In the following description, a <I>pattern-list</I> is a list of oneor more patterns separated by a <B>|</B>.Composite patterns may be formed using one or more of the followingsub-patterns:<P> <DL COMPACT><DT><DD><DL COMPACT><DT><B>?(</B><I>pattern-list</I><B>)</B><DD>Matches zero or one occurrence of the given patterns<DT><B>*(</B><I>pattern-list</I><B>)</B><DD>Matches zero or more occurrences of the given patterns<DT><B>+(</B><I>pattern-list</I><B>)</B><DD>Matches one or more occurrences of the given patterns<DT><B>@(</B><I>pattern-list</I><B>)</B><DD>Matches one of the given patterns<DT><B>!(</B><I>pattern-list</I><B>)</B><DD>Matches anything except one of the given patterns</DL></DL>  <P> The<B>extglob</B> option changes the behavior of the parser, since theparentheses are normally treated as operators with syntactic meaning.To ensure that extended matching patterns are parsed correctly, make surethat <B>extglob</B> is enabled before parsing constructs containing thepatterns, including shell functions and command substitutions.<P> When matching filenames, the <B>dotglob</B> shell option determinesthe set of filenames that are tested:when <B>dotglob</B> is enabled, the set of filenames includes all filesbeginning with ``.'', but ``.'' and ``..'' must be matched by apattern or sub-pattern that begins with a dot;when it is disabled, the set does notinclude any filenames beginning with ``.'' unless the patternor sub-pattern begins with a ``.''.As above, ``.'' only has a special meaning when matching filenames.<P> Complicated extended pattern matching against long strings is slow,especially when the patterns contain alternations and the stringscontain multiple matches.Using separate matches against shorter strings, or using arrays ofstrings instead of a single long string, may be faster.<A NAME="lbBH">&nbsp;</A><H4>Quote Removal</H4> After the preceding expansions, all unquoted occurrences of thecharacters<B>\</B>, <B>aq</B>, and <B>&quot;</B> that did not result from one of the aboveexpansions are removed.<A NAME="lbBI">&nbsp;</A><H3>REDIRECTION</H3> Before a command is executed, its input and outputmay be<I>redirected</I> using a special notation interpreted by the shell.<I>Redirection</I> allows commands' file handles to beduplicated, opened, closed,made to refer to different files,and can change the files the command reads from and writes to.Redirection may also be used to modify file handles in thecurrent shell execution environment.The following redirectionoperators may precede or appear anywhere within a<I>simple command</I> or may follow a<I>command</I>. Redirections are processed in the order they appear, fromleft to right.<P> Each redirection that may be preceded by a file descriptor numbermay instead be preceded by a word of the form {<I>varname</I>}.In this case, for each redirection operator except&gt;&amp;- and &lt;&amp;-, the shell will allocate a file descriptor greaterthan or equal to 10 and assign it to <I>varname</I>.If &gt;&amp;- or &lt;&amp;- is precededby {<I>varname</I>}, the value of <I>varname</I> defines the filedescriptor to close.If {<I>varname</I>} is supplied, the redirection persists beyondthe scope of the command, allowing the shell programmer to managethe file descriptor's lifetime manually.The <B>varredir_close</B> shell option manages this behavior.<P> In the following descriptions, if the file descriptor number isomitted, and the first character of the redirection operator is<B>&lt;</B>, the redirection refers to the standard input (file descriptor0).  If the first character of the redirection operator is<B>&gt;</B>, the redirection refers to the standard output (file descriptor1).<P> The word following the redirection operator in the followingdescriptions, unless otherwise noted, is subjected tobrace expansion, tilde expansion, parameter and variable expansion,command substitution, arithmetic expansion, quote removal,pathname expansion, and word splitting.If it expands to more than one word,<B>bash</B> reports an error.<P> Note that the order of redirections is significant.  For example,the command<DL COMPACT><DT><DD><P> ls <B>&gt;</B> dirlist 2<B>&gt;&amp;</B>1</DL> <P> directs both standard output and standard error to the file<I>dirlist</I>, while the command<DL COMPACT><DT><DD><P> ls 2<B>&gt;&amp;</B>1 <B>&gt;</B> dirlist</DL> <P> directs only the standard output to file<I>dirlist</I>, because the standard error was duplicated from the standard outputbefore the standard output was redirected to<I>dirlist</I>. <P> <B>Bash</B> handles several filenames specially when they are used inredirections, as described in the following table.If the operating system on which <B>bash</B> is running provides thesespecial files, bash will use them; otherwise it will emulate theminternally with the behavior described below.<DL COMPACT><DT><DD><P>  <DL COMPACT><DT><B>/dev/fd/</B><I>fd</I> <DD>If <I>fd</I> is a valid integer, file descriptor <I>fd</I> is duplicated.<DT><B>/dev/stdin</B> <DD>File descriptor 0 is duplicated.<DT><B>/dev/stdout</B> <DD>File descriptor 1 is duplicated.<DT><B>/dev/stderr</B> <DD>File descriptor 2 is duplicated.<DT><B>/dev/tcp/</B><I>host</I>/<I>port</I> <DD>If <I>host</I> is a valid hostname or Internet address, and <I>port</I>is an integer port number or service name, <B>bash</B> attempts to openthe corresponding TCP socket.<DT><B>/dev/udp/</B><I>host</I>/<I>port</I> <DD>If <I>host</I> is a valid hostname or Internet address, and <I>port</I>is an integer port number or service name, <B>bash</B> attempts to openthe corresponding UDP socket. </DL></DL> <P> A failure to open or create a file causes the redirection to fail.<P> Redirections using file descriptors greater than 9 should be used withcare, as they may conflict with file descriptors the shell usesinternally.<A NAME="lbBJ">&nbsp;</A><H4>Redirecting Input</H4> Redirection of input causes the file whose name results fromthe expansion of<I>word</I> to be opened for reading on file descriptor<I>n</I>, or the standard input (file descriptor 0) if<I>n</I> is not specified.<P> The general format for redirecting input is:<DL COMPACT><DT><DD><P> [<I>n</I>]<B>&lt;</B><I>word</I></DL> <A NAME="lbBK">&nbsp;</A><H4>Redirecting Output</H4> Redirection of output causes the file whose name results fromthe expansion of<I>word</I> to be opened for writing on file descriptor<I>n</I>, or the standard output (file descriptor 1) if<I>n</I> is not specified.  If the file does not exist it is created;if it does exist it is truncated to zero size.<P> The general format for redirecting output is:<DL COMPACT><DT><DD><P> [<I>n</I>]<B>&gt;</B><I>word</I></DL> <P> If the redirection operator is<B>&gt;</B>, and the<B>noclobber</B> option to the<B>set</B> builtin has been enabled, the redirection will fail if the filewhose name results from the expansion of <I>word</I> exists and isa regular file.If the redirection operator is<B>&gt;|</B>, or the redirection operator is<B>&gt;</B> and the<B>noclobber</B> option to the<B>set</B> builtin command is not enabled, the redirection is attempted evenif the file named by <I>word</I> exists.<A NAME="lbBL">&nbsp;</A><H4>Appending Redirected Output</H4> Redirection of output in this fashioncauses the file whose name results fromthe expansion of<I>word</I> to be opened for appending on file descriptor<I>n</I>, or the standard output (file descriptor 1) if<I>n</I> is not specified.  If the file does not exist it is created.<P> The general format for appending output is:<DL COMPACT><DT><DD><P> [<I>n</I>]<B>&gt;&gt;</B><I>word</I></DL> <A NAME="lbBM">&nbsp;</A><H4>Redirecting Standard Output and Standard Error</H4> This construct allows both thestandard output (file descriptor 1) andthe standard error output (file descriptor 2)to be redirected to the file whose name is theexpansion of<I>word</I>. <P> There are two formats for redirecting standard output andstandard error:<DL COMPACT><DT><DD><P> <B>&amp;&gt;</B><I>word</I></DL> and<DL COMPACT><DT><DD><B>&gt;&amp;</B><I>word</I></DL> <P> Of the two forms, the first is preferred.This is semantically equivalent to<DL COMPACT><DT><DD><P> <B>&gt;</B><I>word</I> 2<B>&gt;&amp;</B>1</DL> <P> When using the second form, <I>word</I> may not expand to a number or<B>-</B>.  If it does, other redirection operators apply(see <B>Duplicating File Descriptors</B> below) for compatibilityreasons.<A NAME="lbBN">&nbsp;</A><H4>Appending Standard Output and Standard Error</H4> This construct allows both thestandard output (file descriptor 1) andthe standard error output (file descriptor 2)to be appended to the file whose name is theexpansion of<I>word</I>. <P> The format for appending standard output and standard error is:<DL COMPACT><DT><DD><P> <B>&amp;&gt;&gt;</B><I>word</I></DL> <P> This is semantically equivalent to<DL COMPACT><DT><DD><P> <B>&gt;&gt;</B><I>word</I> 2<B>&gt;&amp;</B>1</DL> <P> (see <B>Duplicating File Descriptors</B> below).<A NAME="lbBO">&nbsp;</A><H4>Here Documents</H4> This type of redirection instructs the shell to read input from thecurrent source until a line containing only<I>delimiter</I> (with no trailing blanks)is seen.  All ofthe lines read up to that point are then used as the standardinput (or file descriptor <I>n</I> if <I>n</I> is specified) for a command.<P> The format of here-documents is:<DL COMPACT><DT><DD><P> <PRE>[<I>n</I>]<B>&lt;&lt;</B>[<B>-</B>]<I>word</I>        <I>here-document</I><I>delimiter</I></PRE> </DL> <P> No parameter and variable expansion, command substitution,arithmetic expansion, or pathname expansion is performed on<I>word</I>. If any part of<I>word</I> is quoted, the<I>delimiter</I> is the result of quote removal on<I>word</I>, and the lines in the here-document are not expanded.If <I>word</I> is unquoted,all lines of the here-document are subjected toparameter expansion, command substitution, and arithmetic expansion,the character sequence<B>\&lt;newline&gt;</B> is ignored, and<B>\</B> must be used to quote the characters<B>\</B>, <B>$</B>, and<B>`</B>. <P> If the redirection operator is<B>&lt;&lt;-</B>, then all leading tab characters are stripped from input lines and theline containing<I>delimiter</I>. This allowshere-documents within shell scripts to be indented in anatural fashion.<A NAME="lbBP">&nbsp;</A><H4>Here Strings</H4> A variant of here documents, the format is:<DL COMPACT><DT><DD><P> <PRE>[<I>n</I>]<B>&lt;&lt;&lt;</B><I>word</I></PRE> </DL> <P> The <I>word</I> undergoestilde expansion, parameter and variable expansion,command substitution, arithmetic expansion, and quote removal.Pathname expansion and word splitting are not performed.The result is supplied as a single string, with a newline appended,to the command on itsstandard input (or file descriptor <I>n</I> if <I>n</I> is specified).<A NAME="lbBQ">&nbsp;</A><H4>Duplicating File Descriptors</H4> The redirection operator<DL COMPACT><DT><DD><P> [<I>n</I>]<B>&lt;&amp;</B><I>word</I></DL> <P> is used to duplicate input file descriptors.If<I>word</I> expands to one or more digits, the file descriptor denoted by<I>n</I> is made to be a copy of that file descriptor.If the digits in<I>word</I> do not specify a file descriptor open for input, a redirection error occurs.If<I>word</I> evaluates to<B>-</B>, file descriptor<I>n</I> is closed.  If<I>n</I> is not specified, the standard input (file descriptor 0) is used.<P> The operator<DL COMPACT><DT><DD><P> [<I>n</I>]<B>&gt;&amp;</B><I>word</I></DL> <P> is used similarly to duplicate output file descriptors.  If<I>n</I> is not specified, the standard output (file descriptor 1) is used.If the digits in<I>word</I> do not specify a file descriptor open for output, a redirection error occurs.If<I>word</I> evaluates to<B>-</B>, file descriptor<I>n</I> is closed.As a special case, if <I>n</I> is omitted, and <I>word</I> does notexpand to one or more digits or <B>-</B>, the standard output and standarderror are redirected as described previously.<A NAME="lbBR">&nbsp;</A><H4>Moving File Descriptors</H4> The redirection operator<DL COMPACT><DT><DD><P> [<I>n</I>]<B>&lt;&amp;</B><I>digit</I><B>-</B></DL> <P> moves the file descriptor <I>digit</I> to file descriptor<I>n</I>, or the standard input (file descriptor 0) if <I>n</I> is not specified.<I>digit</I> is closed after being duplicated to <I>n</I>.<P> Similarly, the redirection operator<DL COMPACT><DT><DD><P> [<I>n</I>]<B>&gt;&amp;</B><I>digit</I><B>-</B></DL> <P> moves the file descriptor <I>digit</I> to file descriptor<I>n</I>, or the standard output (file descriptor 1) if <I>n</I> is not specified.<A NAME="lbBS">&nbsp;</A><H4>Opening File Descriptors for Reading and Writing</H4> The redirection operator<DL COMPACT><DT><DD><P> [<I>n</I>]<B>&lt;&gt;</B><I>word</I></DL> <P> causes the file whose name is the expansion of<I>word</I> to be opened for both reading and writing on file descriptor<I>n</I>, or on file descriptor 0 if<I>n</I> is not specified.  If the file does not exist, it is created.<A NAME="lbBT">&nbsp;</A><H3>ALIASES</H3> <I>Aliases</I> allow a string to be substituted for a word when it is usedas the first word of a simple command.The shell maintains a list of aliases that may be set and unset with the<B>alias</B> and<B>unalias</B> builtin commands (see<FONT SIZE=-1><B>SHELL BUILTIN COMMANDS</B> </FONT>below).The first word of each simple command, if unquoted,is checked to see if it has analias.  If so, that word is replaced by the text of the alias.The characters <B>/</B>, <B>$</B>, <B>`</B>, and <B>=</B> andany of the shell <I>metacharacters</I> or quoting characterslisted above may not appear in an alias name.The replacement text may contain any valid shell input,including shell metacharacters.The first word of the replacement text is testedfor aliases, but a word that is identical to an alias being expandedis not expanded a second time.This means that one may alias<B>ls</B> to<B>ls -F</B>, for instance, and<B>bash</B> does not try to recursively expand the replacement text.If the last character of the alias value is a<I>blank</I>, then the next commandword following the alias is also checked for alias expansion.<P> Aliases are created and listed with the<B>alias</B> command, and removed with the<B>unalias</B> command.<P> There is no mechanism for using arguments in the replacement text.If arguments are needed, use a shell function (see<FONT SIZE=-1><B>FUNCTIONS</B> </FONT>below).<P> Aliases are not expanded when the shell is not interactive, unlessthe<B>expand_aliases</B> shell option is set using<B>shopt</B> (see the description of<B>shopt</B> under<FONT SIZE=-1><B>SHELL BUILTIN COMMANDS</B></FONT>below).<P> The rules concerning the definition and use of aliases aresomewhat confusing.<B>Bash</B> always reads at least one complete line of input,and all lines that make up a compound command,before executing any of the commands on that line or the compound command.Aliases are expanded when acommand is read, not when it is executed.  Therefore, analias definition appearing on the same line as anothercommand does not take effect until the next line of input is read.The commands following the alias definitionon that line are not affected by the new alias.This behavior is also an issue when functions are executed.Aliases are expanded when a function definition is read,not when the function is executed, because a function definitionis itself a command.  As a consequence, aliasesdefined in a function are not available until after thatfunction is executed.  To be safe, always putalias definitions on a separate line, and do not use<B>alias</B> in compound commands.<P> For almost every purpose, aliases are superseded byshell functions.<A NAME="lbBU">&nbsp;</A><H3>FUNCTIONS</H3> A shell function, defined as described above under<FONT SIZE=-1><B>SHELL GRAMMAR</B>, </FONT>stores a series of commands for later execution.When the name of a shell function is used as a simple command name,the list of commands associated with that function name is executed.Functions are executed in the context of thecurrent shell; no new process is created to interpretthem (contrast this with the execution of a shell script).When a function is executed, the arguments to thefunction become the positional parametersduring its execution.The special parameter<B>#</B> is updated to reflect the change.  Special parameter <B>0</B>is unchanged.The first element of the<FONT SIZE=-1><B>FUNCNAME</B> </FONT>variable is set to the name of the function while the functionis executing.<P> All other aspects of the shell executionenvironment are identical between a function and its callerwith these exceptions: the<FONT SIZE=-1><B>DEBUG</B> </FONT>and<B>RETURN</B> traps (see the description of the<B>trap</B> builtin under<FONT SIZE=-1><B>SHELL BUILTIN COMMANDS</B> </FONT>below) are not inherited unless the function has been given the<B>trace</B> attribute (see the description of the<FONT SIZE=-1><B>declare</B> </FONT>builtin below) or the<B>-o functrace</B> shell option has been enabled withthe <B>set</B> builtin(in which case all functions inherit the <B>DEBUG</B> and <B>RETURN</B> traps),and the<FONT SIZE=-1><B>ERR</B> </FONT>trap is not inherited unless the <B>-o errtrace</B> shell option hasbeen enabled.<P> Variables local to the function may be declared with the<B>local</B> builtin command (<I>local variables</I>).Ordinarily, variables and their valuesare shared between the function and its caller.If a variable is declared <B>local</B>, the variable's visible scopeis restricted to that function and its children (including the functionsit calls).<P> In the following description, the <I>current scope</I> is a currently-executing function.Previous scopes consist of that function's caller and so on,back to the &quot;global&quot; scope, where the shell is not executingany shell function.Consequently, a local variable at the current scope is a variabledeclared using the <B>local</B> or <B>declare</B> builtins in thefunction that is currently executing.<P> Local variables &quot;shadow&quot; variables with the same name declared atprevious scopes.For instance, a local variable declared in a functionhides a global variable of the same name: references and assignmentsrefer to the local variable, leaving the global variable unmodified.When the function returns, the global variable is once again visible.<P> The shell uses <I>dynamic scoping</I> to control a variable's visibilitywithin functions.With dynamic scoping, visible variables and their valuesare a result of the sequence of function calls that caused executionto reach the current function.The value of a variable that a function sees dependson its value within its caller, if any, whether that caller isthe &quot;global&quot; scope or another shell function.This is also the value that a local variabledeclaration &quot;shadows&quot;, and the value that is restored when the functionreturns.<P> For example, if a variable <I>var</I> is declared as local in function<I>func1</I>, and <I>func1</I> calls another function <I>func2</I>,references to <I>var</I> made from within <I>func2</I> will resolve to thelocal variable <I>var</I> from <I>func1</I>, shadowing any global variablenamed <I>var</I>.<P> The <B>unset</B> builtin also acts using the same dynamic scope: if avariable is local to the current scope, <B>unset</B> will unset it;otherwise the unset will refer to the variable found in any calling scopeas described above.If a variable at the current local scope is unset, it will remain so(appearing as unset)until it is reset in that scope or until the function returns.Once the function returns, any instance of the variable at a previousscope will become visible.If the unset acts on a variable at a previous scope, any instance of avariable with that name that had been shadowed will become visible(see below how the <B>localvar_unset</B> shell option changes this behavior).<P> The <B>FUNCNEST</B> variable, if set to a numeric value greaterthan 0, defines a maximum function nesting level.  Functioninvocations that exceed the limit cause the entire command toabort.<P> If the builtin command<B>return</B> is executed in a function, the function completes andexecution resumes with the next command after the functioncall.Any command associated with the <B>RETURN</B> trap is executedbefore execution resumes.When a function completes, the values of thepositional parameters and the special parameter<B>#</B> are restored to the values they had prior to the function'sexecution.<P> Function names and definitions may be listed with the<B>-f</B> option to the<B>declare</B> or<B>typeset</B> builtin commands.  The<B>-F</B> option to<B>declare</B> or<B>typeset</B> will list the function names only(and optionally the source file and line number, if the <B>extdebug</B>shell option is enabled).Functions may be exported so that child shell processes(those created when executing a separate shell invocation)automatically have them defined with the<B>-f</B> option to the<B>export</B> builtin.A function definition may be deleted using the <B>-f</B> option tothe<B>unset</B> builtin.<P> Functions may be recursive.The <B>FUNCNEST</B> variable may be used to limit the depth of thefunction call stack and restrict the number of function invocations.By default, no limit is imposed on the number of recursive calls.<A NAME="lbBV">&nbsp;</A><H3>ARITHMETIC EVALUATION</H3> The shell allows arithmetic expressions to be evaluated, undercertain circumstances (see the <B>let</B> and <B>declare</B> builtincommands, the <B>((</B> compound command, and <B>Arithmetic Expansion</B>).Evaluation is done in fixed-width integers with no check for overflow,though division by 0 is trapped and flagged as an error.The operators and their precedence, associativity, and valuesare the same as in the C language.The following list of operators is grouped into levels ofequal-precedence operators.The levels are listed in order of decreasing precedence.<P>  <DL COMPACT><DT><B></B><I>id</I>++ <I>id</I>-- <DD>variable post-increment and post-decrement<DT><B>- +</B> <DD>unary minus and plus<DT><B>++</B><I>id</I> --<I>id</I> <DD>variable pre-increment and pre-decrement<DT><B>! ~</B> <DD>logical and bitwise negation<DT><B>**</B> <DD>exponentiation<DT><B>* / %</B> <DD>multiplication, division, remainder<DT><B>+ -</B> <DD>addition, subtraction<DT><B>&lt;&lt; &gt;&gt;</B> <DD>left and right bitwise shifts<DT><B>&lt;= &gt;= &lt; &gt;</B> <DD>comparison<DT><B>== !=</B> <DD>equality and inequality<DT><B>&amp;</B> <DD>bitwise AND<DT><B>^</B> <DD>bitwise exclusive OR<DT><B>|</B> <DD>bitwise OR<DT><B>&amp;&amp;</B> <DD>logical AND<DT><B>||</B> <DD>logical OR<DT><B></B><I>expr</I>?<I>expr</I>:<I>expr</I> <DD>conditional operator<DT><B>= *= /= %= += -= &lt;&lt;= &gt;&gt;= &amp;= ^= |=</B> <DD>assignment<DT><B></B><I>expr1</I> , <I>expr2</I> <DD>comma </DL><P> Shell variables are allowed as operands; parameter expansion isperformed before the expression is evaluated.Within an expression, shell variables may also be referenced by namewithout using the parameter expansion syntax.A shell variable that is null or unset evaluates to 0 when referencedby name without using the parameter expansion syntax.The value of a variable is evaluated as an arithmetic expressionwhen it is referenced, or when a variable which has been given the<I>integer</I> attribute using <B>declare -i</B> is assigned a value.A null value evaluates to 0.A shell variable need not have its <I>integer</I> attributeturned on to be used in an expression.<P> Integer constants follow the C language definition, without suffixes orcharacter constants.Constants with a leading 0 are interpreted as octal numbers.A leading 0x or 0X denotes hexadecimal.Otherwise, numbers take the form [<I>base#</I>]n, where the optional <I>base</I>is a decimal number between 2 and 64 representing the arithmeticbase, and <I>n</I> is a number in that base.If <I>base#</I> is omitted, then base 10 is used.When specifying <I>n</I>,if a non-digit is required,the digits greater than 9 are represented by the lowercase letters,the uppercase letters, @, and _, in that order.If <I>base</I> is less than or equal to 36, lowercase and uppercaseletters may be used interchangeably to represent numbers between 10and 35.<P> Operators are evaluated in order of precedence.  Sub-expressions inparentheses are evaluated first and may override the precedencerules above.<A NAME="lbBW">&nbsp;</A><H3>CONDITIONAL EXPRESSIONS</H3> Conditional expressions are used by the <B>[[</B> compound command andthe <B>test</B> and <B>[</B> builtin commands to test file attributesand perform string and arithmetic comparisons.The <B>test</B> and <B>[</B> commands determine their behavior based onthe number of arguments; see the descriptions of those commands for anyother command-specific actions.<P> Expressions are formed from the following unary or binary primaries.<B>Bash</B> handles several filenames specially when they are used inexpressions.If the operating system on which <B>bash</B> is running provides thesespecial files, bash will use them; otherwise it will emulate theminternally with this behavior:If any <I>file</I> argument to one of the primaries is of the form<I>/dev/fd/n</I>, then file descriptor <I>n</I> is checked.If the <I>file</I> argument to one of the primaries is one of<I>/dev/stdin</I>, <I>/dev/stdout</I>, or <I>/dev/stderr</I>, filedescriptor 0, 1, or 2, respectively, is checked.<P> Unless otherwise specified, primaries that operate on files follow symboliclinks and operate on the target of the link, rather than the link itself.<P>  When used with <B>[[</B>, the <B>&lt;</B> and <B>&gt;</B> operators sortlexicographically using the current locale.The <B>test</B> command sorts using ASCII ordering.<P> <DL COMPACT><DT><B>-a </B><I>file</I> <DD>True if <I>file</I> exists.<DT><B>-b </B><I>file</I> <DD>True if <I>file</I> exists and is a block special file.<DT><B>-c </B><I>file</I> <DD>True if <I>file</I> exists and is a character special file.<DT><B>-d </B><I>file</I> <DD>True if <I>file</I> exists and is a directory.<DT><B>-e </B><I>file</I> <DD>True if <I>file</I> exists.<DT><B>-f </B><I>file</I> <DD>True if <I>file</I> exists and is a regular file.<DT><B>-g </B><I>file</I> <DD>True if <I>file</I> exists and is set-group-id.<DT><B>-h </B><I>file</I> <DD>True if <I>file</I> exists and is a symbolic link.<DT><B>-k </B><I>file</I> <DD>True if <I>file</I> exists and its ``sticky'' bit is set.<DT><B>-p </B><I>file</I> <DD>True if <I>file</I> exists and is a named pipe (FIFO).<DT><B>-r </B><I>file</I> <DD>True if <I>file</I> exists and is readable.<DT><B>-s </B><I>file</I> <DD>True if <I>file</I> exists and has a size greater than zero.<DT><B>-t </B><I>fd</I> <DD>True if file descriptor<I>fd</I> is open and refers to a terminal.<DT><B>-u </B><I>file</I> <DD>True if <I>file</I> exists and its set-user-id bit is set.<DT><B>-w </B><I>file</I> <DD>True if <I>file</I> exists and is writable.<DT><B>-x </B><I>file</I> <DD>True if <I>file</I> exists and is executable.<DT><B>-G </B><I>file</I> <DD>True if <I>file</I> exists and is owned by the effective group id.<DT><B>-L </B><I>file</I> <DD>True if <I>file</I> exists and is a symbolic link.<DT><B>-N </B><I>file</I> <DD>True if <I>file</I> exists and has been modified since it was last read.<DT><B>-O </B><I>file</I> <DD>True if <I>file</I> exists and is owned by the effective user id.<DT><B>-S </B><I>file</I> <DD>True if <I>file</I> exists and is a socket.<DT><I>file1</I> <B>-ef</B> <I>file2</I><DD>True if <I>file1</I> and <I>file2</I> refer to the same device andinode numbers.<DT><I>file1</I> -<B>nt</B> <I>file2</I><DD>True if <I>file1</I> is newer (according to modification date) than <I>file2</I>,or if <I>file1</I> exists and file2 does not.<DT><I>file1</I> -<B>ot</B> <I>file2</I><DD>True if <I>file1</I> is older than <I>file2</I>, or if <I>file2</I> existsand <I>file1</I> does not.<DT><B>-o </B><I>optname</I> <DD>True if the shell option<I>optname</I> is enabled.See the list of options under the description of the<B>-o</B> option to the<B>set</B> builtin below.<DT><B>-v </B><I>varname</I> <DD>True if the shell variable<I>varname</I> is set (has been assigned a value).<DT><B>-R </B><I>varname</I> <DD>True if the shell variable<I>varname</I> is set and is a name reference.<DT><B>-z </B><I>string</I> <DD>True if the length of <I>string</I> is zero.<DT><I>string</I><DD> <DT><B>-n </B><I>string</I> <DD> True if the length of<I>string</I> is non-zero.<DT><I>string1</I> <B>==</B> <I>string2</I><DD> <DT><I>string1</I> <B>=</B> <I>string2</I><DD> True if the strings are equal.  <B>=</B> should be usedwith the <B>test</B> command for POSIX conformance.When used with the <B>[[</B> command, this performs pattern matching asdescribed above (<B>Compound Commands</B>).<DT><I>string1</I> <B>!=</B> <I>string2</I><DD>True if the strings are not equal.<DT><I>string1</I> <B>&lt;</B> <I>string2</I><DD>True if <I>string1</I> sorts before <I>string2</I> lexicographically.<DT><I>string1</I> <B>&gt;</B> <I>string2</I><DD>True if <I>string1</I> sorts after <I>string2</I> lexicographically.<DT><I>arg1</I> <B>OP</B> <I>arg2</I> <DD><FONT SIZE=-1><B>OP</B> </FONT>is one of<B>-eq</B>, <B>-ne</B>, <B>-lt</B>, <B>-le</B>, <B>-gt</B>, or<B>-ge</B>. These arithmetic binary operators return true if <I>arg1</I>is equal to, not equal to, less than, less than or equal to,greater than, or greater than or equal to <I>arg2</I>, respectively.<I>Arg1</I> and<I>arg2</I> may be positive or negative integers.When used with the <B>[[</B> command,<I>Arg1</I> and<I>Arg2</I> are evaluated as arithmetic expressions (see<FONT SIZE=-1><B>ARITHMETIC EVALUATION</B> </FONT>above). </DL><A NAME="lbBX">&nbsp;</A><H3>SIMPLE COMMAND EXPANSION</H3> When a simple command is executed, the shell performs the followingexpansions, assignments, and redirections, from left to right, inthe following order.<DL COMPACT><DT>1.<DD>The words that the parser has marked as variable assignments (thosepreceding the command name) and redirections are saved for laterprocessing.<DT>2.<DD>The words that are not variable assignments or redirections areexpanded.  If any words remain after expansion, the first wordis taken to be the name of the command and the remaining words arethe arguments.<DT>3.<DD>Redirections are performed as described above under<FONT SIZE=-1><B>REDIRECTION</B>. </FONT><DT>4.<DD>The text after the <B>=</B> in each variable assignment undergoes tildeexpansion, parameter expansion, command substitution, arithmetic expansion,and quote removal before being assigned to the variable.</DL><P> If no command name results, the variable assignments affect the currentshell environment.In the case of such a command (one that consists only of assignmentstatements and redirections), assignment statements are performed beforeredirections.Otherwise, the variables are added to the environmentof the executed command and do not affect the current shell environment.If any of the assignments attempts to assign a value to a readonly variable,an error occurs, and the command exits with a non-zero status.<P> If no command name results, redirections are performed, but do notaffect the current shell environment.  A redirection error causes thecommand to exit with a non-zero status.<P> If there is a command name left after expansion, execution proceeds asdescribed below.  Otherwise, the command exits.  If one of the expansionscontained a command substitution, the exit status of the command isthe exit status of the last command substitution performed.  If therewere no command substitutions, the command exits with a status of zero.<A NAME="lbBY">&nbsp;</A><H3>COMMAND EXECUTION</H3> After a command has been split into words, if it results in asimple command and an optional list of arguments, the followingactions are taken.<P> If the command name contains no slashes, the shell attempts tolocate it.  If there exists a shell function by that name, thatfunction is invoked as described above in<FONT SIZE=-1><B>FUNCTIONS</B>. </FONT>If the name does not match a function, the shell searches forit in the list of shell builtins.  If a match is found, thatbuiltin is invoked.<P> If the name is neither a shell function nor a builtin,and contains no slashes,<B>bash</B> searches each element of the<FONT SIZE=-1><B>PATH</B> </FONT>for a directory containing an executable file by that name.<B>Bash</B> uses a hash table to remember the full pathnames of executablefiles (see<B>hash</B> under<FONT SIZE=-1><B>SHELL BUILTIN COMMANDS</B> </FONT>below).A full search of the directories in<FONT SIZE=-1><B>PATH</B> </FONT>is performed only if the command is not found in the hash table.If the search is unsuccessful, the shell searches for a defined shellfunction named <B>command_not_found_handle</B>.If that function exists, it is invoked in a separate execution environmentwith the original command andthe original command's arguments as its arguments, and the function'sexit status becomes the exit status of that subshell.If that function is not defined, the shell prints an errormessage and returns an exit status of 127.<P> If the search is successful, or if the command name containsone or more slashes, the shell executes the named program in aseparate execution environment.Argument 0 is set to the name given, and the remaining argumentsto the command are set to the arguments given, if any.<P> If this execution fails because the file is not in executableformat, and the file is not a directory, it is assumed to bea <I>shell script</I>, a filecontaining shell commands, and the shell creates anew instance of itselfto execute it.This subshell reinitializes itself, sothat the effect is as if a new shell had been invokedto handle the script, with the exception that the locations ofcommands remembered by the parent (see<B>hash</B> below under<FONT SIZE=-1><B>SHELL BUILTIN COMMANDS</B>)</FONT>are retained by the child.<P> If the program is a file beginning with<B>#!</B>, the remainder of the first line specifies an interpreterfor the program.  The shell executes thespecified interpreter on operating systems that do nothandle this executable format themselves.  The arguments to theinterpreter consist of a single optional argument following theinterpreter name on the first line of the program, followedby the name of the program, followed by the commandarguments, if any.<A NAME="lbBZ">&nbsp;</A><H3>COMMAND EXECUTION ENVIRONMENT</H3> The shell has an <I>execution environment</I>, which consists of thefollowing:<DL COMPACT><DT>*<DD>open files inherited by the shell at invocation, as modified byredirections supplied to the <B>exec</B> builtin<DT>*<DD>the current working directory as set by <B>cd</B>, <B>pushd</B>, or<B>popd</B>, or inherited by the shell at invocation<DT>*<DD>the file creation mode mask as set by <B>umask</B> or inherited fromthe shell's parent<DT>*<DD>current traps set by <B>trap</B><DT>*<DD>shell parameters that are set by variable assignment or with <B>set</B>or inherited from the shell's parent in the environment<DT>*<DD>shell functions defined during execution or inherited from the shell'sparent in the environment<DT>*<DD>options enabled at invocation (either by default or with command-linearguments) or by <B>set</B><DT>*<DD>options enabled by <B>shopt</B><DT>*<DD>shell aliases defined with <B>alias</B><DT>*<DD>various process IDs, including those of background jobs, the valueof <B>$$</B>, and the value of<FONT SIZE=-1><B>PPID</B> </FONT></DL><P> When a simple command other than a builtin or shell functionis to be executed, itis invoked in a separate execution environment that consists ofthe following.Unless otherwise noted, the values are inherited from the shell. <DL COMPACT><DT>*<DD>the shell's open files, plus any modifications and additions specifiedby redirections to the command<DT>*<DD>the current working directory<DT>*<DD>the file creation mode mask<DT>*<DD>shell variables and functions marked for export, along with variablesexported for the command, passed in the environment<DT>*<DD>traps caught by the shell are reset to the values inherited from theshell's parent, and traps ignored by the shell are ignored</DL><P> A command invoked in this separate environment cannot affect theshell's execution environment.<P> A <I>subshell</I> is a copy of the shell process.<P> Command substitution, commands grouped with parentheses,and asynchronous commands are invoked in asubshell environment that is a duplicate of the shell environment,except that traps caught by the shell are reset to the valuesthat the shell inherited from its parent at invocation.  Builtincommands that are invoked as part of a pipeline are also executed in asubshell environment.  Changes made to the subshell environmentcannot affect the shell's execution environment.<P> Subshells spawned to execute command substitutions inherit the value ofthe <B>-e</B> option from the parent shell.  When not in <I>posix mode</I>,<B>bash</B> clears the <B>-e</B> option in such subshells.<P> If a command is followed by a <B>&amp;</B> and job control is not active, thedefault standard input for the command is the empty file <I>/dev/null</I>.Otherwise, the invoked command inherits the file descriptors of the callingshell as modified by redirections.<A NAME="lbCA">&nbsp;</A><H3>ENVIRONMENT</H3> When a program is invoked it is given an array of stringscalled the<I>environment</I>. This is a list of<I>name</I>-<I>value</I> pairs, of the form<I>name</I>=value. <P> The shell provides several ways to manipulate the environment.On invocation, the shell scans its own environment andcreates a parameter for each name found, automatically markingit for<I>export</I> to child processes.  Executed commands inherit the environment.The<B>export</B> and<B>declare -x</B> commands allow parameters and functions to be added to anddeleted from the environment.  If the value of a parameterin the environment is modified, the new value becomes partof the environment, replacing the old.  The environmentinherited by any executed command consists of the shell'sinitial environment, whose values may be modified in the shell,less any pairs removed by the<B>unset</B> command, plus any additions via the<B>export</B> and<B>declare -x</B> commands.<P> The environment for any<I>simple command</I> or function may be augmented temporarily by prefixing it withparameter assignments, as described above in<FONT SIZE=-1><B>PARAMETERS</B>. </FONT>These assignment statements affect only the environment seenby that command.<P> If the<B>-k</B> option is set (see the<B>set</B> builtin command below), then<I>all</I> parameter assignments are placed in the environment for a command,not just those that precede the command name.<P> When<B>bash</B> invokes an external command, the variable<B>_</B> is set to the full filename of the command and passed to thatcommand in its environment.<A NAME="lbCB">&nbsp;</A><H3>EXIT STATUS</H3> The exit status of an executed command is the value returned by the<I>waitpid</I> system call or equivalent function.  Exit statusesfall between 0 and 255, though, as explained below, the shell mayuse values above 125 specially.  Exit statuses from shell builtins andcompound commands are also limited to this range.  Under certaincircumstances, the shell will use special values to indicate specificfailure modes.<P> For the shell's purposes, a command which exits with azero exit status has succeeded.  An exit status of zeroindicates success.  A non-zero exit status indicates failure.When a command terminates on a fatal signal <I>N</I>, <B>bash</B> usesthe value of 128+<I>N</I> as the exit status.<P> If a command is not found, the child process created toexecute it returns a status of 127.  If a command is foundbut is not executable, the return status is 126.<P> If a command fails because of an error during expansion or redirection,the exit status is greater than zero.<P> Shell builtin commands return a status of 0 (<I>true</I>) ifsuccessful, and non-zero (<I>false</I>) if an error occurswhile they execute.All builtins return an exit status of 2 to indicate incorrect usage,generally invalid options or missing arguments.<P> The exit status of the last command is available in the specialparameter $?.<P> <B>Bash</B> itself returns the exit status of the last commandexecuted, unless a syntax error occurs, in which case it exitswith a non-zero value.  See also the <B>exit</B> builtincommand below.<A NAME="lbCC">&nbsp;</A><H3>SIGNALS</H3> When <B>bash</B> is interactive, in the absence of any traps, it ignores<FONT SIZE=-1><B>SIGTERM</B> </FONT>(so that <B>kill 0</B> does not kill an interactive shell),and<FONT SIZE=-1><B>SIGINT</B> </FONT>is caught and handled (so that the <B>wait</B> builtin is interruptible).In all cases, <B>bash</B> ignores<FONT SIZE=-1><B>SIGQUIT</B>. </FONT>If job control is in effect,<B>bash</B> ignores<FONT SIZE=-1><B>SIGTTIN</B>, </FONT><FONT SIZE=-1><B>SIGTTOU</B>, </FONT>and<FONT SIZE=-1><B>SIGTSTP</B>. </FONT><P> Non-builtin commands run by <B>bash</B> have signal handlersset to the values inherited by the shell from its parent.When job control is not in effect, asynchronous commandsignore<FONT SIZE=-1><B>SIGINT</B> </FONT>and<FONT SIZE=-1><B>SIGQUIT</B> </FONT>in addition to these inherited handlers.Commands run as a result of command substitution ignore thekeyboard-generated job control signals<FONT SIZE=-1><B>SIGTTIN</B>, </FONT><FONT SIZE=-1><B>SIGTTOU</B>, </FONT>and<FONT SIZE=-1><B>SIGTSTP</B>. </FONT><P> The shell exits by default upon receipt of a<FONT SIZE=-1><B>SIGHUP</B>. </FONT>Before exiting, an interactive shell resends the<FONT SIZE=-1><B>SIGHUP</B> </FONT>to all jobs, running or stopped.Stopped jobs are sent<FONT SIZE=-1><B>SIGCONT</B> </FONT>to ensure that they receive the<FONT SIZE=-1><B>SIGHUP</B>. </FONT>To prevent the shell fromsending the signal to a particular job, it should be removed from thejobs table with the<B>disown</B> builtin (see<FONT SIZE=-1><B>SHELL BUILTIN COMMANDS</B> </FONT>below) or markedto not receive<FONT SIZE=-1><B>SIGHUP</B> </FONT>using<B>disown -h</B>. <P> If the<B>huponexit</B> shell option has been set with<B>shopt</B>, <B>bash</B> sends a<FONT SIZE=-1><B>SIGHUP</B> </FONT>to all jobs when an interactive login shell exits.<P> If <B>bash</B> is waiting for a command to complete and receives a signalfor which a trap has been set, the trap will not be executed untilthe command completes.When <B>bash</B> is waiting for an asynchronous command via the <B>wait</B>builtin, the reception of a signal for which a trap has been set willcause the <B>wait</B> builtin to return immediately with an exit statusgreater than 128, immediately after which the trap is executed.<P> When job control is not enabled, and <B>bash</B> is waiting for a foregroundcommand to complete, the shell receives keyboard-generated signalssuch as<FONT SIZE=-1><B>SIGINT</B> </FONT>(usually generated by <B>^C</B>) that users commonly intend to sendto that command.This happens because the shell and the command are in thesame process group as the terminal, and <B>^C</B> sends<FONT SIZE=-1><B>SIGINT</B> </FONT>to all processes in that process group.<P> When <B>bash</B> is running without job control enabled and receives <FONT SIZE=-1><B>SIGINT</B> </FONT>while waiting for a foreground command, it waits until that foregroundcommand terminates and then decides what to do about the<FONT SIZE=-1><B>SIGINT</B>: </FONT><DL COMPACT><DT>1.<DD>If the command terminates due to the<FONT SIZE=-1><B>SIGINT</B>, </FONT><B>bash</B> concludesthat the user meant to end the entire script, and acts on the<FONT SIZE=-1><B>SIGINT</B> </FONT>(e.g., by running a<FONT SIZE=-1><B>SIGINT</B> </FONT>trap or exiting itself);<DT>2.<DD>If the command does not terminate due to<FONT SIZE=-1><B>SIGINT</B>, </FONT>the program handled the<FONT SIZE=-1><B>SIGINT</B> </FONT>itself and did not treat it as a fatal signal.In that case, <B>bash</B> does not treat<FONT SIZE=-1><B>SIGINT</B> </FONT>as a fatal signal, either, instead assuming that the<FONT SIZE=-1><B>SIGINT</B> </FONT>was used as part of the program's normal operation(e.g., emacs uses it to abort editingcommands) or deliberately discarded.However, <B>bash</B> will run anytrap set on<FONT SIZE=-1><B>SIGINT</B>, </FONT>as it does with any other trapped signal itreceives while it is waiting for the foreground command tocomplete, for compatibility.</DL><A NAME="lbCD">&nbsp;</A><H3>JOB CONTROL</H3> <I>Job control</I> refers to the ability to selectively stop (<I>suspend</I>)the execution of processes and continue (<I>resume</I>)their execution at a later point.  A user typically employsthis facility via an interactive interface supplied jointlyby the operating system kernel's terminal driver and<B>bash</B>. <P> The shell associates a<I>job</I> with each pipeline.  It keeps a table of currently executingjobs, which may be listed with the<B>jobs</B> command.  When<B>bash</B> starts a job asynchronously (in the<I>background</I>), it prints a line that looks like:<DL COMPACT><DT><DD><P> [1] 25647</DL> <P> indicating that this job is job number 1 and that the process IDof the last process in the pipeline associated with this job is 25647.All of the processes in a single pipeline are members of the same job.<B>Bash</B> uses the<I>job</I> abstraction as the basis for job control.<P> To facilitate the implementation of the user interface to jobcontrol, the operating system maintains the notion of a <I>current terminalprocess group ID</I>.  Members of this process group (processes whoseprocess group ID is equal to the current terminal process group ID)receive keyboard-generated signals such as<FONT SIZE=-1><B>SIGINT</B>. </FONT>These processes are said to be in the<I>foreground</I>. <I>Background</I> processes are those whose process group ID differs from the terminal's;such processes are immune to keyboard-generated signals.Only foreground processes are allowed to read from or, if theuser so specifies with <TT>stty tostop</TT>, write to theterminal.Background processes which attempt to read from (write to when<TT>stty tostop</TT> is in effect) theterminal are sent a<FONT SIZE=-1><B>SIGTTIN (SIGTTOU)</B> </FONT>signal by the kernel's terminal driver,which, unless caught, suspends the process.<P> If the operating system on which<B>bash</B> is running supportsjob control,<B>bash</B> contains facilities to use it.Typing the<I>suspend</I> character (typically<B>^Z</B>, Control-Z) while a process is runningcauses that process to be stopped and returns control to<B>bash</B>. Typing the<I>delayed suspend</I> character (typically<B>^Y</B>, Control-Y) causes the process to be stopped when itattempts to read input from the terminal, and control tobe returned to<B>bash</B>. The user may then manipulate the state of this job, using the<B>bg</B> command to continue it in the background, the<B>fg</B> command to continue it in the foreground, orthe<B>kill</B> command to kill it.  A <B>^Z</B> takes effect immediately,and has the additional side effect of causing pending outputand typeahead to be discarded.<P> There are a number of ways to refer to a job in the shell.The character<B>%</B> introduces a job specification (<I>jobspec</I>).  Job number<I>n</I> may be referred to as<B>%n</B>. A job may also be referred to using a prefix of the name used tostart it, or using a substring that appears in its command line.For example,<B>%ce</B> refers to a stoppedjob whose command name begins with<B>ce</B>. If a prefix matches more than one job,<B>bash</B> reports an error.  Using<B>%?ce</B>, on the other hand, refers to any job containing the string<B>ce</B> in its command line.  If the substring matches more than one job,<B>bash</B> reports an error.  The symbols<B>%%</B> and<B>%+</B> refer to the shell's notion of the<I>current job</I>, which is the last job stopped while it was inthe foreground or started in the background.The<I>previous job</I> may be referenced using<B>%-</B>. If there is only a single job, <B>%+</B> and <B>%-</B> can both be usedto refer to that job.In output pertaining to jobs (e.g., the output of the<B>jobs</B> command), the current job is always flagged with a<B>+</B>, and the previous job with a<B>-</B>. A single % (with no accompanying job specification) also refers to thecurrent job.<P> Simply naming a job can be used to bring it into theforeground:<B>%1</B> is a synonym for<B>``fg %1''</B>,bringing job 1 from the background into the foreground.Similarly,<B>``%1 &amp;''</B> resumes job 1 in the background, equivalent to<B>``bg %1''</B>.<P> The shell learns immediately whenever a job changes state.Normally,<B>bash</B> waits until it is about to print a prompt before reportingchanges in a job's status so as to not interruptany other output.  If the<B>-b</B> option to the<B>set</B> builtin commandis enabled,<B>bash</B> reports such changes immediately.Any trap on<FONT SIZE=-1><B>SIGCHLD</B> </FONT>is executed for each child that exits.<P> If an attempt to exit<B>bash</B> is made while jobs are stopped (or, if the <B>checkjobs</B> shell option hasbeen enabled using the <B>shopt</B> builtin, running), the shell prints awarning message, and, if the <B>checkjobs</B> option is enabled, lists thejobs and their statuses.The<B>jobs</B> command may then be used to inspect their status.If a second attempt to exit is made without an intervening command,the shell does not print another warning, and any stoppedjobs are terminated.<P> When the shell is waiting for a job or process using the <B>wait</B>builtin, and job control is enabled, <B>wait</B> will return when thejob changes state. The <B>-f</B> option causes <B>wait</B> to waituntil the job or process terminates before returning.<A NAME="lbCE">&nbsp;</A><H3>PROMPTING</H3> When executing interactively,<B>bash</B> displays the primary prompt<FONT SIZE=-1><B>PS1</B> </FONT>when it is ready to read a command, and the secondary prompt<FONT SIZE=-1><B>PS2</B> </FONT>when it needs more input to complete a command.<B>Bash</B> displays<FONT SIZE=-1><B>PS0</B> </FONT>after it reads a command but before executing it.<B>Bash</B> displays<FONT SIZE=-1><B>PS4</B> </FONT>as described abovebefore tracing each command when the <B>-x</B> option is enabled.<B>Bash</B> allows these prompt strings to be customized by inserting a number ofbackslash-escaped special characters that are decoded as follows:<DL COMPACT><DT><DD> <DL COMPACT><DT><B>\a</B> <DD>an ASCII bell character (07)<DT><B>\d</B> <DD>the date in &quot;Weekday Month Date&quot; format (e.g., &quot;Tue May 26&quot;)<DT><B>\D{</B><I>format</I>} <DD>the <I>format</I> is passed to <I>strftime</I>(3) and the result is insertedinto the prompt string; an empty <I>format</I> results in a locale-specifictime representation.  The braces are required<DT><B>\e</B> <DD>an ASCII escape character (033)<DT><B>\h</B> <DD>the hostname up to the first `.'<DT><B>\H</B> <DD>the hostname<DT><B>\j</B> <DD>the number of jobs currently managed by the shell<DT><B>\l</B> <DD>the basename of the shell's terminal device name<DT><B>\n</B> <DD>newline<DT><B>\r</B> <DD>carriage return<DT><B>\s</B> <DD>the name of the shell, the basename of<B>$0</B> (the portion following the final slash)<DT><B>\t</B> <DD>the current time in 24-hour HH:MM:SS format<DT><B>\T</B> <DD>the current time in 12-hour HH:MM:SS format<DT><B>\@</B> <DD>the current time in 12-hour am/pm format<DT><B>\A</B> <DD>the current time in 24-hour HH:MM format<DT><B>\u</B> <DD>the username of the current user<DT><B>\v</B> <DD>the version of <B>bash</B> (e.g., 2.00)<DT><B>\V</B> <DD>the release of <B>bash</B>, version + patch level (e.g., 2.00.0)<DT><B>\w</B> <DD>the value of the <B>PWD</B> shell variable (<B>$PWD</B>),with<FONT SIZE=-1><B>$HOME</B> </FONT>abbreviated with a tilde(uses the value of the<FONT SIZE=-1><B>PROMPT_DIRTRIM</B> </FONT>variable)<DT><B>\W</B> <DD>the basename of <B>$PWD</B>,with<FONT SIZE=-1><B>$HOME</B> </FONT>abbreviated with a tilde<DT><B>\!</B> <DD>the history number of this command<DT><B>\#</B> <DD>the command number of this command<DT><B>\$</B> <DD>if the effective UID is 0, a<B>#</B>, otherwise a<B>$</B> <DT><B>\</B><I>nnn</I> <DD>the character corresponding to the octal number <I>nnn</I><DT><B>\\</B> <DD>a backslash<DT><B>\[</B> <DD>begin a sequence of non-printing characters, which could be used toembed a terminal control sequence into the prompt<DT><B>\]</B> <DD>end a sequence of non-printing characters </DL></DL> <P> The command number and the history number are usually different:the history number of a command is its position in the historylist, which may include commands restored from the history file(see<FONT SIZE=-1><B>HISTORY</B> </FONT>below), while the command number is the position in the sequenceof commands executed during the current shell session.After the string is decoded, it is expanded viaparameter expansion, command substitution, arithmeticexpansion, and quote removal, subject to the value of the<B>promptvars</B> shell option (see the description of the<B>shopt</B> command under<FONT SIZE=-1><B>SHELL BUILTIN COMMANDS</B> </FONT>below).This can have unwanted side effects if escaped portions of the stringappear within command substitution or contain characters special toword expansion.<A NAME="lbCF">&nbsp;</A><H3>READLINE</H3> This is the library that handles reading input when using an interactiveshell, unless the<B>--noediting</B> option is given at shell invocation.Line editing is also used when using the <B>-e</B> option to the<B>read</B> builtin.By default, the line editing commands are similar to those of Emacs.A vi-style line editing interface is also available.Line editing can be enabled at any time using the<B>-o emacs</B> or<B>-o vi</B> options to the<B>set</B> builtin (see<FONT SIZE=-1><B>SHELL BUILTIN COMMANDS</B> </FONT>below).To turn off line editing after the shell is running, use the<B>+o emacs</B> or<B>+o vi</B> options to the<B>set</B> builtin.<A NAME="lbCG">&nbsp;</A><H4>Readline Notation</H4> In this section, the Emacs-style notation is used to denotekeystrokes.  Control keys are denoted by C-<I>key</I>, e.g., C-nmeans Control-N.  Similarly,<I>meta</I> keys are denoted by M-<I>key</I>, so M-x means Meta-X.  (On keyboardswithout a<I>meta</I> key, M-<I>x</I> means ESC <I>x</I>, i.e., press the Escape keythen the<I>x</I> key.  This makes ESC the <I>meta prefix</I>.The combination M-C-<I>x</I> means ESC-Control-<I>x</I>,or press the Escape keythen hold the Control key while pressing the<I>x</I> key.)<P> Readline commands may be given numeric<I>arguments</I>, which normally act as a repeat count.Sometimes, however, it is the sign of the argument that is significant.Passing a negative argument to a command that acts in the forwarddirection (e.g., <B>kill-line</B>) causes that command to act in abackward direction.Commands whose behavior with arguments deviates from this are notedbelow.<P> When a command is described as <I>killing</I> text, the textdeleted is saved for possible future retrieval(<I>yanking</I>).  The killed text is saved in a<I>kill ring</I>.  Consecutive kills cause the text to beaccumulated into one unit, which can be yanked all at once.Commands which do not kill text separate the chunks of texton the kill ring.<A NAME="lbCH">&nbsp;</A><H4>Readline Initialization</H4> Readline is customized by putting commands in an initializationfile (the <I>inputrc</I> file).The name of this file is taken from the value of the<FONT SIZE=-1><B>INPUTRC</B> </FONT>variable.  If that variable is unset, the default is<A HREF="file:~/.inputrc"><I>~/.inputrc</I></A>. If that file  does not exist or cannot be read, the ultimate default is<A HREF="file:/etc/inputrc"><I>/etc/inputrc</I></A>. When a program which uses the readline library starts up, theinitialization file is read, and the key bindings and variablesare set.There are only a few basic constructs allowed in thereadline initialization file.Blank lines are ignored.Lines beginning with a <B>#</B> are comments.Lines beginning with a <B>$</B> indicate conditional constructs.Other lines denote key bindings and variable settings.<P> The default key-bindings may be changed with an<I>inputrc</I> file.Other programs that use this library may add their own commandsand bindings.<P> For example, placing<DL COMPACT><DT><DD><P> M-Control-u: universal-argument</DL> or<DL COMPACT><DT><DD>C-Meta-u: universal-argument</DL> into the<I>inputrc</I> would make M-C-u execute the readline command<I>universal-argument</I>. <P> The following symbolic character names are recognized:<I>RUBOUT</I>, <I>DEL</I>, <I>ESC</I>, <I>LFD</I>, <I>NEWLINE</I>, <I>RET</I>, <I>RETURN</I>, <I>SPC</I>, <I>SPACE</I>, and<I>TAB</I>. <P> In addition to command names, readline allows keys to be boundto a string that is inserted when the key is pressed (a <I>macro</I>).<A NAME="lbCI">&nbsp;</A><H4>Readline Key Bindings</H4> The syntax for controlling key bindings in the<I>inputrc</I> file is simple.  All that is required is the name of thecommand or the text of a macro and a key sequence to whichit should be bound.  The name may be specified in one of two ways:as a symbolic key name, possibly with <I>Meta-</I> or <I>Control-</I>prefixes, or as a key sequence.<P> When using the form <B>keyname</B>:<I>function-name</I> or <I>macro</I>,<I>keyname</I> is the name of a key spelled out in English.  For example:<P><DL COMPACT><DT><DD>Control-u: universal-argument<BR> Meta-Rubout: backward-kill-word<BR> Control-o: &quot;&gt; output&quot;</DL> <P> In the above example,<I>C-u</I> is bound to the function<B>universal-argument</B>, <I>M-DEL</I> is bound to the function<B>backward-kill-word</B>, and<I>C-o</I> is bound to run the macroexpressed on the right hand side (that is, to insert the text<TT>&gt; output</TT> into the line).<P> In the second form, <B>&quot;keyseq&quot;</B>:<I>function-name</I> or <I>macro</I>,<B>keyseq</B> differs from<B>keyname</B> above in that strings denotingan entire key sequence may be specified by placing the sequencewithin double quotes.  Some GNU Emacs style key escapes can beused, as in the following example, but the symbolic character namesare not recognized.<P><DL COMPACT><DT><DD>&quot;\C-u&quot;: universal-argument<BR> &quot;\C-x\C-r&quot;: re-read-init-file<BR> &quot;\e[11~&quot;: &quot;Function Key 1&quot;</DL> <P> In this example,<I>C-u</I> is again bound to the function<B>universal-argument</B>. <I>C-x C-r</I> is bound to the function<B>re-read-init-file</B>, and<I>ESC [ 1 1 ~</I> is bound to insert the text<TT>Function Key 1</TT>. <P> The full set of GNU Emacs style escape sequences is<DL COMPACT><DT><DD> <DL COMPACT><DT><B>\C-</B> <DD>control prefix<DT><B>\M-</B> <DD>meta prefix<DT><B>\e</B> <DD>an escape character<DT><B>\\</B> <DD>backslash<DT><B>\</B> <DD>literal &quot;<DT><B>\aq</B> <DD>literal aq</DL></DL>  <P> In addition to the GNU Emacs style escape sequences, a secondset of backslash escapes is available:<DL COMPACT><DT><DD> <DL COMPACT><DT><B>\a</B> <DD>alert (bell)<DT><B>\b</B> <DD>backspace<DT><B>\d</B> <DD>delete<DT><B>\f</B> <DD>form feed<DT><B>\n</B> <DD>newline<DT><B>\r</B> <DD>carriage return<DT><B>\t</B> <DD>horizontal tab<DT><B>\v</B> <DD>vertical tab<DT><B>\</B><I>nnn</I> <DD>the eight-bit character whose value is the octal value <I>nnn</I>(one to three digits)<DT><B>\x</B><I>HH</I> <DD>the eight-bit character whose value is the hexadecimal value <I>HH</I>(one or two hex digits)</DL></DL>  <P> When entering the text of a macro, single or double quotes mustbe used to indicate a macro definition.Unquoted text is assumed to be a function name.In the macro body, the backslash escapes described above are expanded.Backslash will quote any other character in the macro text,including &quot; and aq.<P> <B>Bash</B> allows the current readline key bindings to be displayed or modifiedwith the<B>bind</B> builtin command.  The editing mode may be switched during interactiveuse by using the<B>-o</B> option to the<B>set</B> builtin command (see<FONT SIZE=-1><B>SHELL BUILTIN COMMANDS</B> </FONT>below).<A NAME="lbCJ">&nbsp;</A><H4>Readline Variables</H4> Readline has variables that can be used to further customize itsbehavior.  A variable may be set in the<I>inputrc</I> file with a statement of the form<DL COMPACT><DT><DD><P> <B>set</B> <I>variable-name</I> <I>value</I></DL> or using the <B>bind</B> builtin command (see<FONT SIZE=-1><B>SHELL BUILTIN COMMANDS</B> </FONT>below).<P> Except where noted, readline variables can take the values<B>On</B> or<B>Off</B> (without regard to case).Unrecognized variable names are ignored.When a variable value is read, empty or null values, &quot;on&quot; (case-insensitive),and &quot;1&quot; are equivalent to <B>On</B>.  All other values are equivalent to<B>Off</B>.The variables and their default values are:<P>  <DL COMPACT><DT><B>active-region-start-color   </B> <DD>A string variable that controls the text color and background when displayingthe text in the active region (see the description of<B>enable-active-region</B> below).This string must not take up any physical character positions on the display,so it should consist only of terminal escape sequences.It is output to the terminal before displaying the text in the active region.This variable is reset to the default value whenever the terminal type changes.The default value is the string that puts the terminal in standout mode,as obtained from the terminal's terminfo description.A sample value might be <TT>&quot;\e[01;33m&quot;</TT>.<DT><B>active-region-end-color     </B> <DD>A string variable that &quot;undoes&quot; the effects of <B>active-region-start-color</B> and restores &quot;normal&quot; terminal display appearance after displaying textin the active region.This string must not take up any physical character positions on the display,so it should consist only of terminal escape sequences.It is output to the terminal after displaying the text in the active region.This variable is reset to the default value whenever the terminal type changes.The default value is the string that restores the terminal from standout mode,as obtained from the terminal's terminfo description.A sample value might be <TT>&quot;\e[0m&quot;</TT>.<DT><B>bell-style (audible)</B> <DD>Controls what happens when readline wants to ring the terminal bell.If set to <B>none</B>, readline never rings the bell.  If set to<B>visible</B>, readline uses a visible bell if one is available.If set to <B>audible</B>, readline attempts to ring the terminal's bell.<DT><B>bind-tty-special-chars (On)</B> <DD>If set to <B>On</B>, readline attempts to bind the control characterstreated specially by the kernel's terminal driver to their readlineequivalents.<DT><B>blink-matching-paren (Off)</B> <DD>If set to <B>On</B>, readline attempts to briefly move the cursor to anopening parenthesis when a closing parenthesis is inserted.<DT><B>colored-completion-prefix (Off)</B> <DD>If set to <B>On</B>, when listing completions, readline displays thecommon prefix of the set of possible completions using a different color.The color definitions are taken from the value of the <B>LS_COLORS</B>environment variable.If there is a color definition in <B>$LS_COLORS</B> for the custom suffix&quot;readline-colored-completion-prefix&quot;, readline uses this color forthe common prefix instead of its default.<DT><B>colored-stats (Off)</B> <DD>If set to <B>On</B>, readline displays possible completions using differentcolors to indicate their file type.The color definitions are taken from the value of the <B>LS_COLORS</B>environment variable.<DT><B>comment-begin (``#'')</B> <DD>The string that is inserted when the readline<B>insert-comment</B> command is executed.This command is bound to<B>M-#</B> in emacs mode and to<B>#</B> in vi command mode.<DT><B>completion-display-width (-1)</B> <DD>The number of screen columns used to display possible matcheswhen performing completion.The value is ignored if it is less than 0 or greater than the terminalscreen width.A value of 0 will cause matches to be displayed one per line.The default value is -1.<DT><B>completion-ignore-case (Off)</B> <DD>If set to <B>On</B>, readline performs filename matching and completionin a case-insensitive fashion.<DT><B>completion-map-case (Off)</B> <DD>If set to <B>On</B>, and <B>completion-ignore-case</B> is enabled, readlinetreats hyphens (<I>-</I>) and underscores (<I>_</I>) as equivalent whenperforming case-insensitive filename matching and completion.<DT><B>completion-prefix-display-length (0)</B> <DD>The length in characters of the common prefix of a list of possiblecompletions that is displayed without modification.  When set to avalue greater than zero, common prefixes longer than this value arereplaced with an ellipsis when displaying possible completions.<DT><B>completion-query-items (100)</B> <DD>This determines when the user is queried about viewingthe number of possible completionsgenerated by the <B>possible-completions</B> command.It may be set to any integer value greater than or equal to zero.If the number of possible completions is greater thanor equal to the value of this variable,readline will ask whether or not the user wishes to view them;otherwise they are simply listed on the terminal.A zero value means readline should never ask; negative values aretreated as zero.<DT><B>convert-meta (On)</B> <DD>If set to <B>On</B>, readline will convert characters with theeighth bit set to an ASCII key sequenceby stripping the eighth bit and prefixing anescape character (in effect, using escape as the <I>meta prefix</I>).The default is <I>On</I>, but readline will set it to <I>Off</I> if thelocale contains eight-bit characters.This variable is dependent on the <B>LC_CTYPE</B> locale category, and may change if the locale is changed.<DT><B>disable-completion (Off)</B> <DD>If set to <B>On</B>, readline will inhibit word completion.  Completioncharacters will be inserted into the line as if they had beenmapped to <B>self-insert</B>.<DT><B>echo-control-characters (On)</B> <DD>When set to <B>On</B>, on operating systems that indicate they support it,readline echoes a character corresponding to a signal generated from thekeyboard.<DT><B>editing-mode (emacs)</B> <DD>Controls whether readline begins with a set of key bindings similarto <I>Emacs</I> or <I>vi</I>.<B>editing-mode</B> can be set to either<B>emacs</B> or<B>vi</B>. <DT><B>emacs-mode-string (@)</B> <DD>If the <I>show-mode-in-prompt</I> variable is enabled,this string is displayed immediately before the last line of the primaryprompt when emacs editing mode is active.  The value is expanded like akey binding, so the standard set of meta- and control prefixes andbackslash escape sequences is available.Use the \1 and \2 escapes to begin and end sequences ofnon-printing characters, which can be used to embed a terminal controlsequence into the mode string.<DT><B>enable-active-region (On)</B> <DD>The <I>point</I> is the current cursor position, and <I>mark</I> refers  to a saved cursor position.   The text between the point and mark is referred to as the <I>region</I>.  When this variable is set to <I>On</I>, readline allows certain commandsto designate the region as <I>active</I>.  When the region is active, readline highlights the text in the region usingthe value of the <B>active-region-start-color</B>, which defaults to thestring that enablesthe terminal's standout mode.The active region shows the text inserted by bracketed-paste and anymatching text found by incremental and non-incremental history searches.<DT><B>enable-bracketed-paste (On)</B> <DD>When set to <B>On</B>, readline configures the terminal to insert eachpaste into the editing buffer as a single string of characters, insteadof treating each character as if it had been read from the keyboard.This prevents readline from executing any editing commands bound to keysequences appearing in the pasted text.<DT><B>enable-keypad (Off)</B> <DD>When set to <B>On</B>, readline will try to enable the applicationkeypad when it is called.  Some systems need this to enable thearrow keys.<DT><B>enable-meta-key (On)</B> <DD>When set to <B>On</B>, readline will try to enable any meta modifierkey the terminal claims to support when it is called.  On many terminals,the meta key is used to send eight-bit characters.<DT><B>expand-tilde (Off)</B> <DD>If set to <B>On</B>, tilde expansion is performed when readlineattempts word completion.<DT><B>history-preserve-point (Off)</B> <DD>If set to <B>On</B>, the history code attempts to place point at thesame location on each history line retrieved with <B>previous-history</B>or <B>next-history</B>.<DT><B>history-size (unset)</B> <DD>Set the maximum number of history entries saved in the history list.If set to zero, any existing history entries are deleted and no new entriesare saved.If set to a value less than zero, the number of history entries is notlimited.By default, the number of history entries is set to the value of the<B>HISTSIZE</B> shell variable.If an attempt is made to set <I>history-size</I> to a non-numeric value,the maximum number of history entries will be set to 500.<DT><B>horizontal-scroll-mode (Off)</B> <DD>When set to <B>On</B>, makes readline use a single line for display,scrolling the input horizontally on a single screen line when itbecomes longer than the screen width rather than wrapping to a new line.This setting is automatically enabled for terminals of height 1.<DT><B>input-meta (Off)</B> <DD>If set to <B>On</B>, readline will enable eight-bit input (that is,it will not strip the eighth bit from the characters it reads),regardless of what the terminal claims it can support.  The name<B>meta-flag</B> is a synonym for this variable.The default is <I>Off</I>, but readline will set it to <I>On</I> if thelocale contains eight-bit characters.This variable is dependent on the <B>LC_CTYPE</B> locale category, and may change if the locale is changed.<DT><B>isearch-terminators (``C-[C-J'')</B> <DD>The string of characters that should terminate an incrementalsearch without subsequently executing the character as a command.If this variable has not been given a value, the characters<I>ESC</I> and <I>C-J</I> will terminate an incremental search.<DT><B>keymap (emacs)</B> <DD>Set the current readline keymap.  The set of valid keymap names is<I>emacs, emacs-standard, emacs-meta, emacs-ctlx, vi,vi-command</I>, and<I>vi-insert</I>. <I>vi</I> is equivalent to <I>vi-command</I>; <I>emacs</I> isequivalent to <I>emacs-standard</I>.  The default value is<I>emacs</I>; the value of<B>editing-mode</B> also affects the default keymap.<DT><B>keyseq-timeout (500)</B> <DD>Specifies the duration <I>readline</I> will wait for a character when reading anambiguous key sequence (one that can form a complete key sequence usingthe input read so far, or can take additional input to complete a longerkey sequence).If no input is received within the timeout, <I>readline</I> will use the shorterbut complete key sequence.The value is specified in milliseconds, so a value of 1000 means that<I>readline</I> will wait one second for additional input.If this variable is set to a value less than or equal to zero, or to anon-numeric value, <I>readline</I> will wait until another key is pressed todecide which key sequence to complete.<DT><B>mark-directories (On)</B> <DD>If set to <B>On</B>, completed directory names have a slashappended.<DT><B>mark-modified-lines (Off)</B> <DD>If set to <B>On</B>, history lines that have been modified are displayedwith a preceding asterisk (<B>*</B>).<DT><B>mark-symlinked-directories (Off)</B> <DD>If set to <B>On</B>, completed names which are symbolic links to directorieshave a slash appended (subject to the value of<B>mark-directories</B>).<DT><B>match-hidden-files (On)</B> <DD>This variable, when set to <B>On</B>, causes readline to match files whosenames begin with a `.' (hidden files) when performing filenamecompletion.If set to <B>Off</B>, the leading `.' must besupplied by the user in the filename to be completed.<DT><B>menu-complete-display-prefix (Off)</B> <DD>If set to <B>On</B>, menu completion displays the common prefix of thelist of possible completions (which may be empty) before cycling throughthe list.<DT><B>output-meta (Off)</B> <DD>If set to <B>On</B>, readline will display characters with theeighth bit set directly rather than as a meta-prefixed escapesequence.The default is <I>Off</I>, but readline will set it to <I>On</I> if thelocale contains eight-bit characters.This variable is dependent on the <B>LC_CTYPE</B> locale category, and may change if the locale is changed.<DT><B>page-completions (On)</B> <DD>If set to <B>On</B>, readline uses an internal <I>more</I>-like pagerto display a screenful of possible completions at a time.<DT><B>print-completions-horizontally (Off)</B> <DD>If set to <B>On</B>, readline will display completions with matchessorted horizontally in alphabetical order, rather than down the screen.<DT><B>revert-all-at-newline (Off)</B> <DD>If set to <B>On</B>, readline will undo all changes to history linesbefore returning when <B>accept-line</B> is executed.  By default,history lines may be modified and retain individual undo lists acrosscalls to <B>readline</B>.<DT><B>show-all-if-ambiguous (Off)</B> <DD>This alters the default behavior of the completion functions.  Ifset to<B>On</B>, words which have more than one possible completion cause thematches to be listed immediately instead of ringing the bell.<DT><B>show-all-if-unmodified (Off)</B> <DD>This alters the default behavior of the completion functions ina fashion similar to <B>show-all-if-ambiguous</B>.If set to<B>On</B>, words which have more than one possible completion without anypossible partial completion (the possible completions don't sharea common prefix) cause the matches to be listed immediately insteadof ringing the bell.<DT><B>show-mode-in-prompt (Off)</B> <DD>If set to <B>On</B>, add a string to the beginning of the promptindicating the editing mode: emacs, vi command, or vi insertion.The mode strings are user-settable (e.g., <I>emacs-mode-string</I>).<DT><B>skip-completed-text (Off)</B> <DD>If set to <B>On</B>, this alters the default completion behavior wheninserting a single match into the line.  It's only active whenperforming completion in the middle of a word.  If enabled, readlinedoes not insert characters from the completion that match charactersafter point in the word being completed, so portions of the wordfollowing the cursor are not duplicated.<DT><B>vi-cmd-mode-string ((cmd))</B> <DD>If the <I>show-mode-in-prompt</I> variable is enabled,this string is displayed immediately before the last line of the primaryprompt when vi editing mode is active and in command mode.The value is expanded like akey binding, so the standard set of meta- and control prefixes andbackslash escape sequences is available.Use the \1 and \2 escapes to begin and end sequences ofnon-printing characters, which can be used to embed a terminal controlsequence into the mode string.<DT><B>vi-ins-mode-string ((ins))</B> <DD>If the <I>show-mode-in-prompt</I> variable is enabled,this string is displayed immediately before the last line of the primaryprompt when vi editing mode is active and in insertion mode.The value is expanded like akey binding, so the standard set of meta- and control prefixes andbackslash escape sequences is available.Use the \1 and \2 escapes to begin and end sequences ofnon-printing characters, which can be used to embed a terminal controlsequence into the mode string.<DT><B>visible-stats (Off)</B> <DD>If set to <B>On</B>, a character denoting a file's type as reportedby <I>stat</I>(2) is appended to the filename when listing possiblecompletions. </DL><A NAME="lbCK">&nbsp;</A><H4>Readline Conditional Constructs</H4> Readline implements a facility similar in spirit to the conditionalcompilation features of the C preprocessor which allows keybindings and variable settings to be performed as the resultof tests.  There are four parser directives used.<DL COMPACT><DT><B>$if</B><DD>The<B>$if</B> construct allows bindings to be made based on theediting mode, the terminal being used, or the application usingreadline.  The text of the test, after any comparison operator,<BR>&nbsp;extends&nbsp;to&nbsp;the&nbsp;end&nbsp;of&nbsp;the&nbsp;line;unless otherwise noted, no characters are required to isolate it.<DL COMPACT><DT><DD><DL COMPACT><DT><B>mode</B><DD>The <B>mode=</B> form of the <B>$if</B> directive is used to testwhether readline is in emacs or vi mode.This may be used in conjunctionwith the <B>set keymap</B> command, for instance, to set bindings inthe <I>emacs-standard</I> and <I>emacs-ctlx</I> keymaps only ifreadline is starting out in emacs mode.<DT><B>term</B><DD>The <B>term=</B> form may be used to include terminal-specifickey bindings, perhaps to bind the key sequences output by theterminal's function keys.  The word on the right side of the<B>=</B> is tested against both the full name of the terminal and the portionof the terminal name before the first <B>-</B>.  This allows<I>sun</I> to match both<I>sun</I> and<I>sun-cmd</I>, for instance.<DT><B>version</B><DD>The <B>version</B> test may be used to perform comparisons againstspecific readline versions.The <B>version</B> expands to the current readline version.The set of comparison operators includes<B>=</B>, (and<B>==</B>), <B>!=</B>, <B>&lt;=</B>, <B>&gt;=</B>, <B>&lt;</B>, and<B>&gt;</B>. The version number supplied on the right side of the operator consistsof a major version number, an optional decimal point, and an optionalminor version (e.g., <B>7.1</B>). If the minor version is omitted, itis assumed to be <B>0</B>.The operator may be separated from the string <B>version</B>and from the version number argument by whitespace.<DT><B>application</B><DD>The <B>application</B> construct is used to includeapplication-specific settings.  Each program using the readlinelibrary sets the <I>application name</I>, and an initializationfile can test for a particular value.This could be used to bind key sequences to functions useful fora specific program.  For instance, the following command adds akey sequence that quotes the current or previous word in <B>bash</B>:<P><DL COMPACT><DT><DD><PRE><B>$if</B> Bash# Quote the current or previous word&quot;\C-xq&quot;: &quot;\eb\&quot;\ef\&quot;&quot;<B>$endif</B></PRE> </DL> <DT><I>variable</I><DD>The <I>variable</I> construct provides simple equality tests for readlinevariables and values.The permitted comparison operators are <I>=</I>, <I>==</I>, and <I>!=</I>.The variable name must be separated from the comparison operator bywhitespace; the operator may be separated from the value on the right handside by whitespace.Both string and boolean variables may be tested. Boolean variables must betested against the values <I>on</I> and <I>off</I>.</DL></DL> <DT><B>$endif</B><DD>This command, as seen in the previous example, terminates an<B>$if</B> command.<DT><B>$else</B><DD>Commands in this branch of the <B>$if</B> directive are executed ifthe test fails.<DT><B>$include</B><DD>This directive takes a single filename as an argument and reads commandsand bindings from that file.  For example, the following directivewould read <A HREF="file:/etc/inputrc"><I>/etc/inputrc</I></A>:<P><DL COMPACT><DT><DD><PRE><B>$include</B>  <A HREF="file:/etc/inputrc"><I>/etc/inputrc</I></A></PRE> </DL> </DL><A NAME="lbCL">&nbsp;</A><H4>Searching</H4> Readline provides commands for searching through the command history(see<FONT SIZE=-1><B>HISTORY</B> </FONT>below) for lines containing a specified string.There are two search modes:<I>incremental</I> and<I>non-incremental</I>. <P> Incremental searches begin before the user has finished typing thesearch string.As each character of the search string is typed, readline displaysthe next entry from the history matching the string typed so far.An incremental search requires only as many characters as needed tofind the desired history entry.The characters present in the value of the <B>isearch-terminators</B>variable are used to terminate an incremental search.If that variable has not been assigned a value the Escape andControl-J characters will terminate an incremental search.Control-G will abort an incremental search and restore the originalline.When the search is terminated, the history entry containing thesearch string becomes the current line.<P> To find other matching entries in the history list, type Control-S orControl-R as appropriate.This will search backward or forward in the history for the nextentry matching the search string typed so far.Any other key sequence bound to a readline command will terminatethe search and execute that command.For instance, a <I>newline</I> will terminate the search and acceptthe line, thereby executing the command from the history list.<P> Readline remembers the last incremental search string.  If twoControl-Rs are typed without any intervening characters defining anew search string, any remembered search string is used.<P> Non-incremental searches read the entire search string before startingto search for matching history lines.  The search string may betyped by the user or be part of the contents of the current line.<A NAME="lbCM">&nbsp;</A><H4>Readline Command Names</H4> The following is a list of the names of the commands and the defaultkey sequences to which they are bound.Command names without an accompanying key sequence are unbound by default.In the following descriptions, <I>point</I> refers to the current cursorposition, and <I>mark</I> refers to a cursor position saved by the<B>set-mark</B> command.The text between the point and mark is referred to as the <I>region</I>.<A NAME="lbCN">&nbsp;</A><H4>Commands for Moving</H4>  <DL COMPACT><DT><B>beginning-of-line (C-a)</B> <DD>Move to the start of the current line.<DT><B>end-of-line (C-e)</B> <DD>Move to the end of the line.<DT><B>forward-char (C-f)</B> <DD>Move forward a character.<DT><B>backward-char (C-b)</B> <DD>Move back a character.<DT><B>forward-word (M-f)</B> <DD>Move forward to the end of the next word.  Words are composed ofalphanumeric characters (letters and digits).<DT><B>backward-word (M-b)</B> <DD>Move back to the start of the current or previous word.Words are composed of alphanumeric characters (letters and digits).<DT><B>shell-forward-word</B> <DD>Move forward to the end of the next word.Words are delimited by non-quoted shell metacharacters.<DT><B>shell-backward-word</B> <DD>Move back to the start of the current or previous word.Words are delimited by non-quoted shell metacharacters.<DT><B>previous-screen-line</B> <DD>Attempt to move point to the same physical screen column on the previousphysical screen line. This will not have the desired effect if the currentreadline line does not take up more than one physical line or if point is notgreater than the length of the prompt plus the screen width.<DT><B>next-screen-line</B> <DD>Attempt to move point to the same physical screen column on the nextphysical screen line. This will not have the desired effect if the currentreadline line does not take up more than one physical line or if the lengthof the current readline line is not greater than the length of the promptplus the screen width.<DT><B>clear-display (M-C-l)</B> <DD>Clear the screen and, if possible, the terminal's scrollback buffer,then redraw the current line,leaving the current line at the top of the screen.<DT><B>clear-screen (C-l)</B> <DD>Clear the screen,then redraw the current line,leaving the current line at the top of the screen.With an argument, refresh the current line without clearing thescreen.<DT><B>redraw-current-line</B> <DD>Refresh the current line. </DL><A NAME="lbCO">&nbsp;</A><H4>Commands for Manipulating the History</H4>  <DL COMPACT><DT><B>accept-line (Newline, Return)</B> <DD>Accept the line regardless of where the cursor is.  If this line isnon-empty, add it to the history list according to the state of the<FONT SIZE=-1><B>HISTCONTROL</B> </FONT>variable.  If the line is a modified historyline, then restore the history line to its original state.<DT><B>previous-history (C-p)</B> <DD>Fetch the previous command from the history list, moving back inthe list.<DT><B>next-history (C-n)</B> <DD>Fetch the next command from the history list, moving forward in thelist.<DT><B>beginning-of-history (M-&lt;)</B> <DD>Move to the first line in the history.<DT><B>end-of-history (M-&gt;)</B> <DD>Move to the end of the input history, i.e., the line currently beingentered.<DT><B>operate-and-get-next (C-o)</B> <DD>Accept the current line for execution and fetch the next linerelative to the current line from the history for editing.A numeric argument, if supplied, specifies the history entry to use insteadof the current line.<DT><B>fetch-history</B> <DD>With a numeric argument, fetch that entry from the history listand make it the current line.Without an argument, move back to the first entry in the history list.<DT><B>reverse-search-history (C-r)</B> <DD>Search backward starting at the current line and moving `up' throughthe history as necessary.  This is an incremental search.<DT><B>forward-search-history (C-s)</B> <DD>Search forward starting at the current line and moving `down' throughthe history as necessary.  This is an incremental search.<DT><B>non-incremental-reverse-search-history (M-p)</B> <DD>Search backward through the history starting at the current lineusing a non-incremental search for a string supplied by the user.<DT><B>non-incremental-forward-search-history (M-n)</B> <DD>Search forward through the history using a non-incremental search fora string supplied by the user.<DT><B>history-search-forward</B> <DD>Search forward through the history for the string of charactersbetween the start of the current line and the point.This is a non-incremental search.<DT><B>history-search-backward</B> <DD>Search backward through the history for the string of charactersbetween the start of the current line and the point.This is a non-incremental search.<DT><B>history-substring-search-backward</B> <DD>Search backward through the history for the string of charactersbetween the start of the current line and the current cursorposition (the <I>point</I>).The search string may match anywhere in a history line.This is a non-incremental search.<DT><B>history-substring-search-forward</B> <DD>Search forward through the history for the string of charactersbetween the start of the current line and the point.The search string may match anywhere in a history line.This is a non-incremental search.<DT><B>yank-nth-arg (M-C-y)</B> <DD>Insert the first argument to the previous command (usuallythe second word on the previous line) at point.With an argument<I>n</I>, insert the <I>n</I>th word from the previous command (the wordsin the previous command begin with word 0).  A negative argumentinserts the <I>n</I>th word from the end of the previous command.Once the argument <I>n</I> is computed, the argument is extractedas if the &quot;!<I>n</I>&quot; history expansion had been specified.<DT><B>yank-last-arg (M-., M-_)</B> <DD>Insert the last argument to the previous command (the last word ofthe previous history entry).With a numeric argument, behave exactly like <B>yank-nth-arg</B>.Successive calls to <B>yank-last-arg</B> move back through the historylist, inserting the last word (or the word specified by the argument tothe first call) of each line in turn.Any numeric argument supplied to these successive calls determinesthe direction to move through the history.  A negative argument switchesthe direction through the history (back or forward).The history expansion facilities are used to extract the last word,as if the &quot;!$&quot; history expansion had been specified.<DT><B>shell-expand-line (M-C-e)</B> <DD>Expand the line as the shell does.  Thisperforms alias and history expansion as well as all of the shellword expansions.  See<FONT SIZE=-1><B>HISTORY EXPANSION</B> </FONT>below for a description of history expansion.<DT><B>history-expand-line (M-^)</B> <DD>Perform history expansion on the current line.See<FONT SIZE=-1><B>HISTORY EXPANSION</B> </FONT>below for a description of history expansion.<DT><B>magic-space</B> <DD>Perform history expansion on the current line and insert a space.See<FONT SIZE=-1><B>HISTORY EXPANSION</B> </FONT>below for a description of history expansion.<DT><B>alias-expand-line</B> <DD>Perform alias expansion on the current line.See<FONT SIZE=-1><B>ALIASES</B> </FONT>above for a description of alias expansion.<DT><B>history-and-alias-expand-line</B> <DD>Perform history and alias expansion on the current line.<DT><B>insert-last-argument (M-., M-_)</B> <DD>A synonym for <B>yank-last-arg</B>.<DT><B>edit-and-execute-command (C-x C-e)</B> <DD>Invoke an editor on the current command line, and execute the result as shellcommands.<B>Bash</B> attempts to invoke<FONT SIZE=-1><B>$VISUAL</B>, </FONT><FONT SIZE=-1><B>$EDITOR</B>, </FONT>and <I>emacs</I> as the editor, in that order. </DL><A NAME="lbCP">&nbsp;</A><H4>Commands for Changing Text</H4>  <DL COMPACT><DT><B></B><I>end-of-file</I> (usually C-d) <DD>The character indicating end-of-file as set, for example, by<TT>stty</TT>. If this character is read when there are no characterson the line, and point is at the beginning of the line, readlineinterprets it as the end of input and returns<FONT SIZE=-1><B>EOF</B>. </FONT><DT><B>delete-char (C-d)</B> <DD>Delete the character at point.If this function is bound to thesame character as the tty <B>EOF</B> character, as <B>C-d</B>commonly is, see above for the effects.<DT><B>backward-delete-char (Rubout)</B> <DD>Delete the character behind the cursor.  When given a numeric argument,save the deleted text on the kill ring.<DT><B>forward-backward-delete-char</B> <DD>Delete the character under the cursor, unless the cursor is at theend of the line, in which case the character behind the cursor isdeleted.<DT><B>quoted-insert (C-q, C-v)</B> <DD>Add the next character typed to the line verbatim.  This ishow to insert characters like <B>C-q</B>, for example.<DT><B>tab-insert (C-v TAB)</B> <DD>Insert a tab character.<DT><B>self-insert (a,&nbsp;b,&nbsp;A,&nbsp;1,&nbsp;!,&nbsp;...)</B> <DD>Insert the character typed.<DT><B>transpose-chars (C-t)</B> <DD>Drag the character before point forward over the character at point,moving point forward as well.If point is at the end of the line, then this transposesthe two characters before point.Negative arguments have no effect.<DT><B>transpose-words (M-t)</B> <DD>Drag the word before point past the word after point,moving point over that word as well.If point is at the end of the line, this transposesthe last two words on the line.<DT><B>upcase-word (M-u)</B> <DD>Uppercase the current (or following) word.  With a negative argument,uppercase the previous word, but do not move point.<DT><B>downcase-word (M-l)</B> <DD>Lowercase the current (or following) word.  With a negative argument,lowercase the previous word, but do not move point.<DT><B>capitalize-word (M-c)</B> <DD>Capitalize the current (or following) word.  With a negative argument,capitalize the previous word, but do not move point.<DT><B>overwrite-mode</B> <DD>Toggle overwrite mode.  With an explicit positive numeric argument,switches to overwrite mode.  With an explicit non-positive numericargument, switches to insert mode.  This command affects only<B>emacs</B> mode; <B>vi</B> mode does overwrite differently.Each call to <I>readline()</I> starts in insert mode.In overwrite mode, characters bound to <B>self-insert</B> replacethe text at point rather than pushing the text to the right.Characters bound to <B>backward-delete-char</B> replace the characterbefore point with a space.  By default, this command is unbound. </DL><A NAME="lbCQ">&nbsp;</A><H4>Killing and Yanking</H4>  <DL COMPACT><DT><B>kill-line (C-k)</B> <DD>Kill the text from point to the end of the line.<DT><B>backward-kill-line (C-x Rubout)</B> <DD>Kill backward to the beginning of the line.<DT><B>unix-line-discard (C-u)</B> <DD>Kill backward from point to the beginning of the line.The killed text is saved on the kill-ring. <DT><B>kill-whole-line</B> <DD>Kill all characters on the current line, no matter where point is.<DT><B>kill-word (M-d)</B> <DD>Kill from point to the end of the current word, or if betweenwords, to the end of the next word.Word boundaries are the same as those used by <B>forward-word</B>.<DT><B>backward-kill-word (M-Rubout)</B> <DD>Kill the word behind point.Word boundaries are the same as those used by <B>backward-word</B>.<DT><B>shell-kill-word</B> <DD>Kill from point to the end of the current word, or if betweenwords, to the end of the next word.Word boundaries are the same as those used by <B>shell-forward-word</B>.<DT><B>shell-backward-kill-word</B> <DD>Kill the word behind point.Word boundaries are the same as those used by <B>shell-backward-word</B>.<DT><B>unix-word-rubout (C-w)</B> <DD>Kill the word behind point, using white space as a word boundary.The killed text is saved on the kill-ring.<DT><B>unix-filename-rubout</B> <DD>Kill the word behind point, using white space and the slash characteras the word boundaries.The killed text is saved on the kill-ring.<DT><B>delete-horizontal-space (M-\)</B> <DD>Delete all spaces and tabs around point.<DT><B>kill-region</B> <DD>Kill the text in the current region.<DT><B>copy-region-as-kill</B> <DD>Copy the text in the region to the kill buffer.<DT><B>copy-backward-word</B> <DD>Copy the word before point to the kill buffer.The word boundaries are the same as <B>backward-word</B>.<DT><B>copy-forward-word</B> <DD>Copy the word following point to the kill buffer.The word boundaries are the same as <B>forward-word</B>.<DT><B>yank (C-y)</B> <DD>Yank the top of the kill ring into the buffer at point.<DT><B>yank-pop (M-y)</B> <DD>Rotate the kill ring, and yank the new top.  Only works following<B>yank</B> or<B>yank-pop</B>.  </DL><A NAME="lbCR">&nbsp;</A><H4>Numeric Arguments</H4>  <DL COMPACT><DT><B>digit-argument (M-0, M-1, ..., M--)</B> <DD>Add this digit to the argument already accumulating, or start a newargument.  M-- starts a negative argument.<DT><B>universal-argument</B> <DD>This is another way to specify an argument.If this command is followed by one or more digits, optionally with aleading minus sign, those digits define the argument.If the command is followed by digits, executing<B>universal-argument</B> again ends the numeric argument, but is otherwise ignored.As a special case, if this command is immediately followed by acharacter that is neither a digit nor minus sign, the argument countfor the next command is multiplied by four.The argument count is initially one, so executing this function thefirst time makes the argument count four, a second time makes theargument count sixteen, and so on. </DL><A NAME="lbCS">&nbsp;</A><H4>Completing</H4>  <DL COMPACT><DT><B>complete (TAB)</B> <DD>Attempt to perform completion on the text before point.<B>Bash</B> attempts completion treating the text as a variable (if thetext begins with <B>$</B>), username (if the text begins with<B>~</B>), hostname (if the text begins with <B>@</B>), orcommand (including aliases and functions) in turn.  If noneof these produces a match, filename completion is attempted.<DT><B>possible-completions (M-?)</B> <DD>List the possible completions of the text before point.<DT><B>insert-completions (M-*)</B> <DD>Insert all completions of the text before pointthat would have been generated by<B>possible-completions</B>.<DT><B>menu-complete</B> <DD>Similar to <B>complete</B>, but replaces the word to be completedwith a single match from the list of possible completions.Repeated execution of <B>menu-complete</B> steps through the listof possible completions, inserting each match in turn.At the end of the list of completions, the bell is rung(subject to the setting of <B>bell-style</B>)and the original text is restored.An argument of <I>n</I> moves <I>n</I> positions forward in the listof matches; a negative argument may be used to move backwardthrough the list.This command is intended to be bound to <B>TAB</B>, but is unboundby default.<DT><B>menu-complete-backward</B> <DD>Identical to <B>menu-complete</B>, but moves backward through the listof possible completions, as if <B>menu-complete</B> had been given anegative argument.  This command is unbound by default.<DT><B>delete-char-or-list</B> <DD>Deletes the character under the cursor if not at the beginning orend of the line (like <B>delete-char</B>).If at the end of the line, behaves identically to<B>possible-completions</B>.This command is unbound by default.<DT><B>complete-filename (M-/)</B> <DD>Attempt filename completion on the text before point.<DT><B>possible-filename-completions (C-x /)</B> <DD>List the possible completions of the text before point,treating it as a filename.<DT><B>complete-username (M-~)</B> <DD>Attempt completion on the text before point, treatingit as a username.<DT><B>possible-username-completions (C-x ~)</B> <DD>List the possible completions of the text before point,treating it as a username.<DT><B>complete-variable (M-$)</B> <DD>Attempt completion on the text before point, treatingit as a shell variable.<DT><B>possible-variable-completions (C-x $)</B> <DD>List the possible completions of the text before point,treating it as a shell variable.<DT><B>complete-hostname (M-@)</B> <DD>Attempt completion on the text before point, treatingit as a hostname.<DT><B>possible-hostname-completions (C-x @)</B> <DD>List the possible completions of the text before point,treating it as a hostname.<DT><B>complete-command (M-!)</B> <DD>Attempt completion on the text before point, treatingit as a command name.  Command completion attempts tomatch the text against aliases, reserved words, shellfunctions, shell builtins, and finally executable filenames,in that order.<DT><B>possible-command-completions (C-x !)</B> <DD>List the possible completions of the text before point,treating it as a command name.<DT><B>dynamic-complete-history (M-TAB)</B> <DD>Attempt completion on the text before point, comparingthe text against lines from the history list for possiblecompletion matches.<DT><B>dabbrev-expand</B> <DD>Attempt menu completion on the text before point, comparingthe text against lines from the history list for possiblecompletion matches.<DT><B>complete-into-braces (M-{)</B> <DD>Perform filename completion and insert the list of possible completionsenclosed within braces so the list is available to the shell (see<B>Brace Expansion</B> above). </DL><A NAME="lbCT">&nbsp;</A><H4>Keyboard Macros</H4>  <DL COMPACT><DT><B>start-kbd-macro (C-x ()</B> <DD>Begin saving the characters typed into the current keyboard macro.<DT><B>end-kbd-macro (C-x ))</B> <DD>Stop saving the characters typed into the current keyboard macroand store the definition.<DT><B>call-last-kbd-macro (C-x e)</B> <DD>Re-execute the last keyboard macro defined, by making the charactersin the macro appear as if typed at the keyboard.<DT><B>print-last-kbd-macro ()</B> <DD>Print the last keyboard macro defined in a format suitable for the<I>inputrc</I> file. </DL><A NAME="lbCU">&nbsp;</A><H4>Miscellaneous</H4>  <DL COMPACT><DT><B>re-read-init-file (C-x C-r)</B> <DD>Read in the contents of the <I>inputrc</I> file, and incorporateany bindings or variable assignments found there.<DT><B>abort (C-g)</B> <DD>Abort the current editing command andring the terminal's bell (subject to the setting of<B>bell-style</B>). <DT><B>do-lowercase-version (M-A, M-B, M-</B><I>x</I>, ...) <DD>If the metafied character <I>x</I> is uppercase, run the commandthat is bound to the corresponding metafied lowercase character.The behavior is undefined if <I>x</I> is already lowercase.<DT><B>prefix-meta (ESC)</B> <DD>Metafy the next character typed.<FONT SIZE=-1><B>ESC</B> </FONT><B>f</B> is equivalent to<B>Meta-f</B>. <DT><B>undo (C-_, C-x C-u)</B> <DD>Incremental undo, separately remembered for each line.<DT><B>revert-line (M-r)</B> <DD>Undo all changes made to this line.  This is like executing the<B>undo</B> command enough times to return the line to its initial state.<DT><B>tilde-expand (M-&amp;)</B> <DD>Perform tilde expansion on the current word.<DT><B>set-mark (C-@, M-&lt;space&gt;)</B> <DD>Set the mark to the point.  If anumeric argument is supplied, the mark is set to that position.<DT><B>exchange-point-and-mark (C-x C-x)</B> <DD>Swap the point with the mark.  The current cursor position is set tothe saved position, and the old cursor position is saved as the mark.<DT><B>character-search (C-])</B> <DD>A character is read and point is moved to the next occurrence of thatcharacter.  A negative argument searches for previous occurrences.<DT><B>character-search-backward (M-C-])</B> <DD>A character is read and point is moved to the previous occurrence of thatcharacter.  A negative argument searches for subsequent occurrences.<DT><B>skip-csi-sequence</B> <DD>Read enough characters to consume a multi-key sequence such as thosedefined for keys like Home and End.  Such sequences begin with aControl Sequence Indicator (CSI), usually ESC-[.  If this sequence isbound to &quot;\[&quot;, keys producing such sequences will have no effectunless explicitly bound to a readline command, instead of insertingstray characters into the editing buffer.  This is unbound by default,but usually bound to ESC-[.<DT><B>insert-comment (M-#)</B> <DD>Without a numeric argument, the value of the readline<B>comment-begin</B> variable is inserted at the beginning of the current line.If a numeric argument is supplied, this command acts as a toggle: ifthe characters at the beginning of the line do not match the valueof <B>comment-begin</B>, the value is inserted, otherwisethe characters in <B>comment-begin</B> are deleted from the beginning ofthe line.In either case, the line is accepted as if a newline had been typed.The default value of<B>comment-begin</B> causes this command to make the current linea shell comment.If a numeric argument causes the comment character to be removed, the linewill be executed by the shell.<DT><B>spell-correct-word (C-x s)</B> <DD>Perform spelling correction on the current word, treating it as a directoryor filename, in the same way as the <B>cdspell</B> shell option.Word boundaries are the same as those used by <B>shell-forward-word</B>.<DT><B>glob-complete-word (M-g)</B> <DD>The word before point is treated as a pattern for pathname expansion,with an asterisk implicitly appended.  This pattern is used togenerate a list of matching filenames for possible completions.<DT><B>glob-expand-word (C-x *)</B> <DD>The word before point is treated as a pattern for pathname expansion,and the list of matching filenames is inserted, replacing the word.If a numeric argument is supplied, an asterisk is appended beforepathname expansion.<DT><B>glob-list-expansions (C-x g)</B> <DD>The list of expansions that would have been generated by<B>glob-expand-word</B> is displayed, and the line is redrawn.If a numeric argument is supplied, an asterisk is appended beforepathname expansion.<DT><B>dump-functions</B> <DD>Print all of the functions and their key bindings to thereadline output stream.  If a numeric argument is supplied,the output is formatted in such a way that it can be made partof an <I>inputrc</I> file.<DT><B>dump-variables</B> <DD>Print all of the settable readline variables and their values to thereadline output stream.  If a numeric argument is supplied,the output is formatted in such a way that it can be made partof an <I>inputrc</I> file.<DT><B>dump-macros</B> <DD>Print all of the readline key sequences bound to macros and thestrings they output.  If a numeric argument is supplied,the output is formatted in such a way that it can be made partof an <I>inputrc</I> file.<DT><B>display-shell-version (C-x C-v)</B> <DD>Display version information about the current instance of<B>bash</B>.  </DL><A NAME="lbCV">&nbsp;</A><H4>Programmable Completion</H4> When word completion is attempted for an argument to a command forwhich a completion specification (a <I>compspec</I>) has been definedusing the <B>complete</B> builtin (see<FONT SIZE=-1><B>SHELL BUILTIN COMMANDS</B> </FONT>below), the programmable completion facilities are invoked.<P> First, the command name is identified.If the command word is the empty string (completion attempted at thebeginning of an empty line), any compspec defined withthe <B>-E</B> option to <B>complete</B> is used.If a compspec has been defined for that command, thecompspec is used to generate the list of possible completions for the word.If the command word is a full pathname, a compspec for the fullpathname is searched for first.If no compspec is found for the full pathname, an attempt is made tofind a compspec for the portion following the final slash.If those searches do not result in a compspec, any compspec defined withthe <B>-D</B> option to <B>complete</B> is used as the default.If there is no default compspec, <B>bash</B> attempts alias expansionon the command word as a final resort, and attempts to find a compspecfor the command word from any successful expansion.<P> Once a compspec has been found, it is used to generate the list ofmatching words.If a compspec is not found, the default <B>bash</B> completion asdescribed above under <B>Completing</B> is performed.<P> First, the actions specified by the compspec are used.Only matches which are prefixed by the word being completed arereturned.When the<B>-f</B> or<B>-d</B> option is used for filename or directory name completion, the shellvariable<FONT SIZE=-1><B>FIGNORE</B> </FONT>is used to filter the matches.<P> Any completions specified by a pathname expansion pattern to the<B>-G</B> option are generated next.The words generated by the pattern need not match the wordbeing completed.The<FONT SIZE=-1><B>GLOBIGNORE</B> </FONT>shell variable is not used to filter the matches, but the<FONT SIZE=-1><B>FIGNORE</B> </FONT>variable is used.<P> Next, the string specified as the argument to the <B>-W</B> optionis considered.The string is first split using the characters in the<FONT SIZE=-1><B>IFS</B> </FONT>special variable as delimiters.Shell quoting is honored.Each word is then expanded usingbrace expansion, tilde expansion, parameter and variable expansion,command substitution, and arithmetic expansion,as described above under<FONT SIZE=-1><B>EXPANSION</B>. </FONT>The results are split using the rules described above under<B>Word Splitting</B>.The results of the expansion are prefix-matched against the word beingcompleted, and the matching words become the possible completions.<P> After these matches have been generated, any shell function or commandspecified with the <B>-F</B> and <B>-C</B> options is invoked.When the command or function is invoked, the<FONT SIZE=-1><B>COMP_LINE</B>, </FONT><FONT SIZE=-1><B>COMP_POINT</B>, </FONT><FONT SIZE=-1><B>COMP_KEY</B>, </FONT>and<FONT SIZE=-1><B>COMP_TYPE</B> </FONT>variables are assigned values as described above under<B>Shell Variables</B>.If a shell function is being invoked, the<FONT SIZE=-1><B>COMP_WORDS</B> </FONT>and<FONT SIZE=-1><B>COMP_CWORD</B> </FONT>variables are also set.When the function or command is invoked,the first argument (<B>$1</B>) is the name of the command whose arguments arebeing completed,the second argument (<B>$2</B>) is the word being completed,and the third argument (<B>$3</B>) is the word preceding the word beingcompleted on the current command line.No filtering of the generated completions against the word being completedis performed; the function or command has complete freedom in generatingthe matches.<P> Any function specified with <B>-F</B> is invoked first.The function may use any of the shell facilities, including the<B>compgen</B> builtin described below, to generate the matches.It must put the possible completions in the<FONT SIZE=-1><B>COMPREPLY</B> </FONT>array variable, one per array element.<P> Next, any command specified with the <B>-C</B> option is invokedin an environment equivalent to command substitution.It should print a list of completions, one per line, to thestandard output.Backslash may be used to escape a newline, if necessary.<P> After all of the possible completions are generated, any filterspecified with the <B>-X</B> option is applied to the list.The filter is a pattern as used for pathname expansion; a <B>&amp;</B>in the pattern is replaced with the text of the word being completed.A literal <B>&amp;</B> may be escaped with a backslash; the backslashis removed before attempting a match.Any completion that matches the pattern will be removed from the list.A leading <B>!</B> negates the pattern; in this case any completionnot matching the pattern will be removed.If the<B>nocasematch</B> shell option is enabled, the match is performed without regard to the caseof alphabetic characters.<P> Finally, any prefix and suffix specified with the <B>-P</B> and <B>-S</B>options are added to each member of the completion list, and the result isreturned to the readline completion code as the list of possiblecompletions.<P> If the previously-applied actions do not generate any matches, and the<B>-o dirnames</B> option was supplied to <B>complete</B> when thecompspec was defined, directory name completion is attempted.<P> If the <B>-o plusdirs</B> option was supplied to <B>complete</B> when thecompspec was defined, directory name completion is attempted and anymatches are added to the results of the other actions.<P> By default, if a compspec is found, whatever it generates is returnedto the completion code as the full set of possible completions.The default <B>bash</B> completions are not attempted, and the readlinedefault of filename completion is disabled.If the <B>-o bashdefault</B> option was supplied to <B>complete</B> whenthe compspec was defined, the <B>bash</B> default completions are attemptedif the compspec generates no matches.If the <B>-o default</B> option was supplied to <B>complete</B> when thecompspec was defined, readline's default completion will be performedif the compspec (and, if attempted, the default <B>bash</B> completions)generate no matches.<P> When a compspec indicates that directory name completion is desired,the programmable completion functions force readline to append a slashto completed names which are symbolic links to directories, subject tothe value of the <B>mark-directories</B> readline variable, regardlessof the setting of the <B>mark-symlinked-directories</B> readline variable.<P> There is some support for dynamically modifying completions.  This ismost useful when used in combination with a default completion specifiedwith <B>complete -D</B>.It's possible for shell functions executed as completionhandlers to indicate that completion should be retried by returning anexit status of 124.  If a shell function returns 124, and changesthe compspec associated with the command on which completion is beingattempted (supplied as the first argument when the function is executed),programmable completion restarts from the beginning, with anattempt to find a new compspec for that command.  This allows a set ofcompletions to be built dynamically as completion is attempted, rather thanbeing loaded all at once.<P> For instance, assuming that there is a library of compspecs, each kept in afile corresponding to the name of the command, the following defaultcompletion function would load completions dynamically:<P> <TT>_completion_loader()<BR> {<BR> <TT>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</TT>. &quot;/etc/bash_completion.d/$1.sh&quot; &gt;/dev/null 2&gt;&amp;1 &amp;&amp; return 124<BR><BR> }<BR> complete -D -F _completion_loader -o bashdefault -o default<BR> </TT><A NAME="lbCW">&nbsp;</A><H3>HISTORY</H3> When the<B>-o history</B> option to the<B>set</B> builtin is enabled, the shell provides access to the<I>command history</I>,the list of commands previously typed.The value of the<FONT SIZE=-1><B>HISTSIZE</B> </FONT>variable is used as thenumber of commands to save in a history list.The text of the last<FONT SIZE=-1><B>HISTSIZE</B> </FONT>commands (default 500) is saved.  The shellstores each command in the history list prior to parameter andvariable expansion (see<FONT SIZE=-1><B>EXPANSION</B> </FONT>above) but after history expansion is performed, subject to thevalues of the shell variables<FONT SIZE=-1><B>HISTIGNORE</B> </FONT>and<FONT SIZE=-1><B>HISTCONTROL</B>. </FONT><P> On startup, the history is initialized from the file named bythe variable<FONT SIZE=-1><B>HISTFILE</B> </FONT>(default <A HREF="file:~/.bash_history"><I>~/.bash_history</I></A>).The file named by the value of<FONT SIZE=-1><B>HISTFILE</B> </FONT>is truncated, if necessary, to contain no more thanthe number of lines specified by the value of<FONT SIZE=-1><B>HISTFILESIZE</B>. </FONT>If <B>HISTFILESIZE</B> is unset, or set to null, a non-numeric value,or a numeric value less than zero, the history file is not truncated.When the history file is read,lines beginning with the history comment character followed immediatelyby a digit are interpreted as timestamps for the following history line.These timestamps are optionally displayed depending on the value of the<FONT SIZE=-1><B>HISTTIMEFORMAT</B> </FONT>variable.When a shell with history enabled exits, the last<FONT SIZE=-1><B>$HISTSIZE</B> </FONT>lines are copied from the history list to<FONT SIZE=-1><B>$HISTFILE</B>. </FONT>If the<B>histappend</B> shell option is enabled(see the description of<B>shopt</B> under<FONT SIZE=-1><B>SHELL BUILTIN COMMANDS</B> </FONT>below), the lines are appended to the history file,otherwise the history file is overwritten.If<FONT SIZE=-1><B>HISTFILE</B> </FONT>is unset, or if the history file is unwritable, the history isnot saved.If the<FONT SIZE=-1><B>HISTTIMEFORMAT</B> </FONT>variable is set, time stamps are written to the history file, markedwith the history comment character, sothey may be preserved across shell sessions.This uses the history comment character to distinguish timestamps fromother history lines.After saving the history, the history file is truncatedto contain no more than<FONT SIZE=-1><B>HISTFILESIZE</B> </FONT>lines.  If<FONT SIZE=-1><B>HISTFILESIZE</B> </FONT>is unset, or set to null, a non-numeric value,or a numeric value less than zero, the history file is not truncated.<P> The builtin command<B>fc</B> (see<FONT SIZE=-1><B>SHELL BUILTIN COMMANDS</B> </FONT>below) may be used to list or edit and re-execute a portion ofthe history list.The<B>history</B> builtin may be used to display or modify the history list andmanipulate the history file.When using command-line editing, search commandsare available in each editing mode that provide access to thehistory list.<P> The shell allows control over which commands are saved on the historylist.  The<FONT SIZE=-1><B>HISTCONTROL</B> </FONT>and<FONT SIZE=-1><B>HISTIGNORE</B> </FONT>variables may be set to cause the shell to save only a subset of thecommands entered.The<B>cmdhist</B> shell option, if enabled, causes the shell to attempt to save eachline of a multi-line command in the same history entry, addingsemicolons where necessary to preserve syntactic correctness.The<B>lithist</B> shell option causes the shell to save the command with embedded newlinesinstead of semicolons.  See the description of the<B>shopt</B> builtin below under<FONT SIZE=-1><B>SHELL BUILTIN COMMANDS</B> </FONT>for information on setting and unsetting shell options.<A NAME="lbCX">&nbsp;</A><H3>HISTORY EXPANSION</H3> The shell supports a history expansion feature thatis similar to the history expansion in<B>csh</B>. This section describes what syntax features are available.  Thisfeature is enabled by default for interactive shells, and can bedisabled using the<B>+H</B> option to the<B>set</B> builtin command (see<FONT SIZE=-1><B>SHELL BUILTIN COMMANDS</B> </FONT>below).  Non-interactive shells do not perform history expansionby default.<P> History expansions introduce words from the history list intothe input stream, making it easy to repeat commands, insert thearguments to a previous command into the current input line, orfix errors in previous commands quickly.<P> History expansion is performed immediately after a complete lineis read, before the shell breaks it into words, and is performedon each line individually without taking quoting on previous lines intoaccount.It takes place in two parts.The first is to determine which line from the history listto use during substitution.The second is to select portions of that line for inclusion intothe current one.The line selected from the history is the <I>event</I>,and the portions of that line that are acted upon are <I>words</I>.Various <I>modifiers</I> are available to manipulate the selected words.The line is broken into words in the same fashion as when reading input,so that several <I>metacharacter</I>-separated words surrounded byquotes are considered one word.History expansions are introduced by the appearance of thehistory expansion character, which is <B>!</B> by default.Only backslash (<B>\</B>) and single quotes can quotethe history expansion character, but the history expansion character isalso treated as quoted if it immediately precedes the closing double quotein a double-quoted string.<P> Several characters inhibit history expansion if found immediatelyfollowing the history expansion character, even if it is unquoted:space, tab, newline, carriage return, and <B>=</B>.If the <B>extglob</B> shell option is enabled, <B>(</B> will alsoinhibit expansion.<P> Several shell options settable with the<B>shopt</B> builtin may be used to tailor the behavior of history expansion.If the<B>histverify</B> shell option is enabled (see the description of the<B>shopt</B> builtin below), and<B>readline</B> is being used, history substitutions are not immediately passed tothe shell parser.Instead, the expanded line is reloaded into the<B>readline</B> editing buffer for further modification.If<B>readline</B> is being used, and the<B>histreedit</B> shell option is enabled, a failed history substitution will be reloadedinto the<B>readline</B> editing buffer for correction.The<B>-p</B> option to the<B>history</B> builtin command may be used to see what a history expansion willdo before using it.The<B>-s</B> option to the<B>history</B> builtin may be used to add commands to the end of the history listwithout actually executing them, so that they are available forsubsequent recall.<P> The shell allows control of the various characters used by thehistory expansion mechanism (see the description of<B>histchars</B> above under<B>Shell Variables</B>). The shell usesthe history comment character to mark history timestamps whenwriting the history file.<A NAME="lbCY">&nbsp;</A><H4>Event Designators</H4> An event designator is a reference to a command line entry in thehistory list.Unless the reference is absolute, events are relative to the currentposition in the history list.<P>  <DL COMPACT><DT><B>!</B> <DD>Start a history substitution, except when followed by a<B>blank</B>, newline, carriage return, =or ( (when the <B>extglob</B> shell option is enabled usingthe <B>shopt</B> builtin).<DT><B>!</B><I>n</I> <DD>Refer to command line<I>n</I>. <DT><B>!-</B><I>n</I> <DD>Refer to the current command minus<I>n</I>. <DT><B>!!</B> <DD>Refer to the previous command.  This is a synonym for `!-1'.<DT><B>!</B><I>string</I> <DD>Refer to the most recent command preceding the current position in thehistory list starting with<I>string</I>. <DT><B>!?</B><I>string</I><B>[?]</B> <DD>Refer to the most recent command preceding the current position in thehistory list containing<I>string</I>. The trailing <B>?</B> may be omitted if<I>string</I> is followed immediately by a newline.If <I>string</I> is missing, the string from the most recent search is used;it is an error if there is no previous search string.<DT><B></B><FONT SIZE=+2><B>^</B></FONT><B></B><I>string1</I><FONT SIZE=+2>^</FONT><I>string2</I><FONT SIZE=+2>^</FONT> <DD>Quick substitution.  Repeat the previous command, replacing<I>string1</I> with<I>string2</I>. Equivalent to``!!:s<FONT SIZE=+2>^</FONT><I>string1</I><FONT SIZE=+2>^</FONT><I>string2</I><FONT SIZE=+2>^</FONT>''(see <B>Modifiers</B> below).<DT><B>!#</B> <DD>The entire command line typed so far. </DL><A NAME="lbCZ">&nbsp;</A><H4>Word Designators</H4> Word designators are used to select desired words from the event.A<B>:</B> separates the event specification from the word designator.It may be omitted if the word designator begins with a<B>^</B>, <B>$</B>, <B>*</B>, <B>-</B>, or<B>%</B>. Words are numbered from the beginning of the line,with the first word being denoted by 0 (zero).Words are inserted into the current line separated by single spaces.<P>  <DL COMPACT><DT><B>0 (zero)</B> <DD>The zeroth word.  For the shell, this is the commandword.<DT><I>n</I> <DD>The <I>n</I>th word.<DT><B>^</B> <DD>The first argument.  That is, word 1.<DT><B>$</B> <DD>The last word.  This is usually the last argument, but will expand to thezeroth word if there is only one word in the line.<DT><B>%</B> <DD>The first word matched by the most recent `?<I>string</I>?' search,if the search string begins with a character that is part of a word.<DT><I>x</I><B>-</B>y <DD>A range of words; `-<I>y</I>' abbreviates `0-<I>y</I>'.<DT><B>*</B> <DD>All of the words but the zeroth.  This is a synonymfor `<I>1-$</I>'.  It is not an error to use<B>*</B> if there is just oneword in the event; the empty string is returned in that case.<DT><B>x*</B> <DD>Abbreviates <I>x-$</I>.<DT><B>x-</B> <DD>Abbreviates <I>x-$</I> like <B>x*</B>, but omits the last word.If <B>x</B> is missing, it defaults to 0. </DL><P> If a word designator is supplied without an event specification, theprevious command is used as the event.<A NAME="lbDA">&nbsp;</A><H4>Modifiers</H4> After the optional word designator, there may appear a sequence ofone or more of the following modifiers, each preceded by a `:'.These modify, or edit, the word or words selected from the history event.<P>  <DL COMPACT><DT><B>h</B> <DD>Remove a trailing filename component, leaving only the head.<DT><B>t</B> <DD>Remove all leading filename components, leaving the tail.<DT><B>r</B> <DD>Remove a trailing suffix of the form <I>.xxx</I>, leaving thebasename.<DT><B>e</B> <DD>Remove all but the trailing suffix.<DT><B>p</B> <DD>Print the new command but do not execute it.<DT><B>q</B> <DD>Quote the substituted words, escaping further substitutions.<DT><B>x</B> <DD>Quote the substituted words as with<B>q</B>, but break into words at<B>blanks</B> and newlines.The <B>q</B> and <B>x</B> modifiers are mutually exclusive; the last onesupplied is used.<DT><B>s/</B><I>old</I>/<I>new</I>/ <DD>Substitute<I>new</I> for the first occurrence of<I>old</I> in the event line.Any character may be used as the delimiter in place of /.The final delimiter is optional if it is the last character of theevent line.The delimiter may be quoted in<I>old</I> and<I>new</I> with a single backslash.  If &amp; appears in<I>new</I>, it is replaced by<I>old</I>. A single backslash will quote the &amp;.If<I>old</I> is null, it is set to the last<I>old</I> substituted, or, if no previous history substitutions took place,the last<I>string</I> in a<B>!?</B><I>string</I><B>[?]</B> search.If<I>new</I> is null, each matching<I>old</I> is deleted.<DT><B>&amp;</B> <DD>Repeat the previous substitution.<DT><B>g</B> <DD>Cause changes to be applied over the entire event line.  This isused in conjunction with `<B>:s</B>' (e.g., `<B>:gs/</B><I>old</I>/<I>new</I>/')or `<B>:&amp;</B>'.  If used with`<B>:s</B>', any delimiter can be usedin place of /, and the final delimiter is optionalif it is the last character of the event line.An <B>a</B> may be used as a synonym for <B>g</B>.<DT><B>G</B> <DD>Apply the following `<B>s</B>' or `<B>&amp;</B>' modifier once to each wordin the event line. </DL><A NAME="lbDB">&nbsp;</A><H3>SHELL BUILTIN COMMANDS</H3>   <P> Unless otherwise noted, each builtin command documented in thissection as accepting options preceded by<B>-</B> accepts<B>--</B> to signify the end of the options.The <B>:</B>, <B>true</B>, <B>false</B>, and <B>test</B>/<B>[</B> builtinsdo not accept options and do not treat <B>--</B> specially.The <B>exit</B>, <B>logout</B>, <B>return</B>,<B>break</B>, <B>continue</B>, <B>let</B>,and <B>shift</B> builtins accept and process arguments beginning with<B>-</B> without requiring <B>--</B>.Other builtins that accept arguments but are not specified as acceptingoptions interpret arguments beginning with <B>-</B> as invalid options andrequire <B>--</B> to prevent this interpretation.<P> <DL COMPACT><DT><B>:</B> [<I>arguments</I>]<DD> No effect; the command does nothing beyond expanding<I>arguments</I> and performing any specifiedredirections.The return status is zero.<DT><B> . </B> <I>filename</I> [<I>arguments</I>]<DD> <DT><B>source</B> <I>filename</I> [<I>arguments</I>]<DD> Read and execute commands from<I>filename</I> in the currentshell environment and return the exit status of the last commandexecuted from<I>filename</I>. If<I>filename</I> does not contain a slash, filenames in<FONT SIZE=-1><B>PATH</B> </FONT>are used to find the directory containing<I>filename</I>, but <I>filename</I> does not need to be executable.The file searched for in<FONT SIZE=-1><B>PATH</B> </FONT>need not be executable.When <B>bash</B> is not in <I>posix mode</I>, it searchesthe current directory if no file is found in<FONT SIZE=-1><B>PATH</B>. </FONT>If the<B>sourcepath</B> option to the<B>shopt</B> builtin command is turned off, the<FONT SIZE=-1><B>PATH</B> </FONT>is not searched.If any <I>arguments</I> are supplied, they become the positionalparameters when <I>filename</I> is executed.  Otherwise the positionalparameters are unchanged.If the <B>-T</B> option is enabled, <B>.</B> inherits any trap on<B>DEBUG</B>; if it is not, any <B>DEBUG</B> trap string is saved andrestored around the call to <B>.</B>, and <B>.</B> unsets the<B>DEBUG</B> trap while it executes.If <B>-T</B> is not set, and the sourced file changesthe <B>DEBUG</B> trap, the new value is retained when <B>.</B> completes.The return status is the status of the last command exited withinthe script (0 if no commands are executed), and false if<I>filename</I> is not found or cannot be read.<DT><B>alias</B> [<B>-p</B>] [<I>name</I>[=<I>value</I>] ...]<DD><B>Alias</B> with no arguments or with the<B>-p</B> option prints the list of aliases in the form<B>alias</B> <I>name</I>=<I>value</I> on standard output.When arguments are supplied, an alias is defined foreach <I>name</I> whose <I>value</I> is given.A trailing space in <I>value</I> causes the next word to bechecked for alias substitution when the alias is expanded.For each <I>name</I> in the argument list for which no <I>value</I>is supplied, the name and value of the alias is printed.<B>Alias</B> returns true unless a <I>name</I> is given for whichno alias has been defined.<DT><B>bg</B> [<I>jobspec</I> ...]<DD>Resume each suspended job <I>jobspec</I> in the background, as if ithad been started with<B>&amp;</B>. If<I>jobspec</I> is not present, the shell's notion of the <I>current job</I> is used.<B>bg</B> <I>jobspec</I> returns 0 unless run when job control is disabled or, when run withjob control enabled, any specified <I>jobspec</I> was not foundor was started without job control.<DT><B>bind</B> [<B>-m</B> <I>keymap</I>] [<B>-lpsvPSVX</B>]<DD> <DT><B>bind</B> [<B>-m</B> <I>keymap</I>] [<B>-q</B> <I>function</I>] [<B>-u</B> <I>function</I>] [<B>-r</B> <I>keyseq</I>]<DD><DT><B>bind</B> [<B>-m</B> <I>keymap</I>] <B>-f</B> <I>filename</I><DD><DT><B>bind</B> [<B>-m</B> <I>keymap</I>] <B>-x</B> <I>keyseq</I>:<I>shell-command</I><DD><DT><B>bind</B> [<B>-m</B> <I>keymap</I>] <I>keyseq</I>:<I>function-name</I><DD><DT><B>bind</B> [<B>-m</B> <I>keymap</I>] <I>keyseq</I>:<I>readline-command</I><DD><DT><B>bind</B> <I>readline-command-line</I><DD> Display current<B>readline</B> key and function bindings, bind a key sequence to a<B>readline</B> function or macro, or set a<B>readline</B> variable.Each non-option argument is a command as it would appear in a<B>readline</B> initialization file such as<I>.inputrc</I>, but each binding or command must be passed as a separate argument;e.g., '&quot;\C-x\C-r&quot;: re-read-init-file'.Options, if supplied, have the following meanings:<DL COMPACT><DT><DD> <DL COMPACT><DT><B>-m </B><I>keymap</I> <DD>Use<I>keymap</I> as the keymap to be affected by the subsequent bindings.Acceptable<I>keymap</I> names are<I>emacs, emacs-standard, emacs-meta, emacs-ctlx, vi,vi-move, vi-command</I>, and<I>vi-insert</I>. <I>vi</I> is equivalent to <I>vi-command</I> (<I>vi-move</I> is alsoa synonym); <I>emacs</I> isequivalent to <I>emacs-standard</I>.<DT><B>-l</B> <DD>List the names of all <B>readline</B> functions.<DT><B>-p</B> <DD>Display <B>readline</B> function names and bindings in such a waythat they can be re-read.<DT><B>-P</B> <DD>List current <B>readline</B> function names and bindings.<DT><B>-s</B> <DD>Display <B>readline</B> key sequences bound to macros and the stringsthey output in such a way that they can be re-read.<DT><B>-S</B> <DD>Display <B>readline</B> key sequences bound to macros and the stringsthey output.<DT><B>-v</B> <DD>Display <B>readline</B> variable names and values in such a way that theycan be re-read.<DT><B>-V</B> <DD>List current <B>readline</B> variable names and values.<DT><B>-f </B><I>filename</I> <DD>Read key bindings from <I>filename</I>.<DT><B>-q </B><I>function</I> <DD>Query about which keys invoke the named <I>function</I>.<DT><B>-u </B><I>function</I> <DD>Unbind all keys bound to the named <I>function</I>.<DT><B>-r </B><I>keyseq</I> <DD>Remove any current binding for <I>keyseq</I>.<DT><B>-x </B><I>keyseq</I>:<I>shell-command</I> <DD>Cause <I>shell-command</I> to be executed whenever <I>keyseq</I> isentered.When <I>shell-command</I> is executed, the shell sets the<FONT SIZE=-1><B>READLINE_LINE</B> </FONT>variable to the contents of the <B>readline</B> line buffer and the<FONT SIZE=-1><B>READLINE_POINT</B> </FONT>and<FONT SIZE=-1><B>READLINE_MARK</B> </FONT>variables to the current location of the insertion point and the savedinsertion point (the mark), respectively.The shell assigns any numeric argument the user supplied to the     <FONT SIZE=-1><B>READLINE_ARGUMENT</B> </FONT>variable.If there was no argument, that variable is not set.If the executed command changes the value of any of<FONT SIZE=-1><B>READLINE_LINE</B>, </FONT><FONT SIZE=-1><B>READLINE_POINT</B>, </FONT>or<FONT SIZE=-1><B>READLINE_MARK</B>, </FONT>those new values will be reflected in the editing state.<DT><B>-X</B> <DD>List all key sequences bound to shell commands and the associated commandsin a format that can be reused as input. </DL><P> The return value is 0 unless an unrecognized option is given or anerror occurred.</DL> <DT><B>break</B> [<I>n</I>]<DD>Exit from within a<B>for</B>, <B>while</B>, <B>until</B>, or<B>select</B> loop.  If <I>n</I> is specified, break <I>n</I> levels.<I>n</I> must be >= 1.  If<I>n</I> is greater than the number of enclosing loops, all enclosing loopsare exited.The return value is 0 unless <I>n</I> is not greater than or equal to 1.<DT><B>builtin</B> <I>shell-builtin</I> [<I>arguments</I>]<DD>Execute the specified shell builtin, passing it<I>arguments</I>, and return its exit status.This is useful when defining afunction whose name is the same as a shell builtin,retaining the functionality of the builtin within the function.The <B>cd</B> builtin is commonly redefined this way.The return status is false if<I>shell-builtin</I> is not a shell builtin command.<DT><B>caller</B> [<I>expr</I>]<DD>Returns the context of any active subroutine call (a shell function ora script executed with the <B>.</B> or <B>source</B> builtins).Without <I>expr</I>, <B>caller</B> displays the line number and sourcefilename of the current subroutine call.If a non-negative integer is supplied as <I>expr</I>, <B>caller</B>displays the line number, subroutine name, and source file correspondingto that position in the current execution call stack.  This extrainformation may be used, for example, to print a stack trace.  Thecurrent frame is frame 0.The return value is 0 unless the shell is not executing a subroutinecall or <I>expr</I> does not correspond to a valid position in thecall stack.<DT><B>cd</B> [<B>-L</B>|[<B>-P</B> [<B>-e</B>]] [-@]] [<I>dir</I>]<DD>Change the current directory to <I>dir</I>.if <I>dir</I> is not supplied, the value of the<FONT SIZE=-1><B>HOME</B> </FONT>shell variable is the default.The variable<FONT SIZE=-1><B>CDPATH</B> </FONT>defines the search path for the directory containing<I>dir</I>: each directory name in<FONT SIZE=-1><B>CDPATH</B> </FONT>is searched for <I>dir</I>.Alternative directory names in<FONT SIZE=-1><B>CDPATH</B> </FONT>are separated by a colon (:).  A null directory name in<FONT SIZE=-1><B>CDPATH</B> </FONT>is the same as the current directory, i.e., ``<B>.</B>''.  If<I>dir</I> begins with a slash (/),then<FONT SIZE=-1><B>CDPATH</B> </FONT>is not used.  The<B>-P</B> option causes <B>cd</B> to use the physical directory structureby resolving symbolic links while traversing <I>dir</I> andbefore processing instances of <I>..</I> in <I>dir</I> (see also the<B>-P</B> option to the<B>set</B> builtin command); the<B>-L</B> option forces symbolic links to be followed by resolving the linkafter processing instances of <I>..</I> in <I>dir</I>.If <I>..</I> appears in <I>dir</I>, it is processed by removing theimmediately previous pathname component from <I>dir</I>, back to a slashor the beginning of <I>dir</I>.If the<B>-e</B> option is supplied with<B>-P</B>, and the current working directory cannot be successfully determinedafter a successful directory change, <B>cd</B> will return an unsuccessfulstatus.On systems that support it, the <B>-@</B> option presents the extendedattributes associated with a file as a directory.An argument of<B>-</B> is converted to<FONT SIZE=-1><B>$OLDPWD</B> </FONT>before the directory change is attempted.If a non-empty directory name from<FONT SIZE=-1><B>CDPATH</B> </FONT>is used, or if<B>-</B> is the first argument, and the directory change issuccessful, the absolute pathname of the new working directory iswritten to the standard output.If the directory change is successful, <B>cd</B> sets the value of the<B>PWD</B> environment variable to the new directory name, and sets the<B>OLDPWD</B> environment variable to the value of the current workingdirectory before the change.The return value is true if the directory was successfully changed;false otherwise.<DT><B>command</B> [<B>-pVv</B>] <I>command</I> [<I>arg</I> ...]<DD>Run<I>command</I> with<I>args</I> suppressing the normal shell function lookup.Only builtin commands or commands found in the<FONT SIZE=-1><B>PATH</B> </FONT>are executed.  If the<B>-p</B> option is given, the search for<I>command</I> is performed using a default value for<FONT SIZE=-1><B>PATH</B> </FONT>that is guaranteed to find all of the standard utilities.If either the<B>-V</B> or<B>-v</B> option is supplied, a description of<I>command</I> is printed.  The<B>-v</B> option causes a single word indicating the command or filenameused to invoke<I>command</I> to be displayed; the<B>-V</B> option produces a more verbose description.If the<B>-V</B> or<B>-v</B> option is supplied, the exit status is 0 if<I>command</I> was found, and 1 if not.  If neither option is supplied andan error occurred or<I>command</I> cannot be found, the exit status is 127.  Otherwise, the exit status of the<B>command</B> builtin is the exit status of<I>command</I>. <DT><B>compgen</B> [<I>option</I>] [<I>word</I>]<DD>Generate possible completion matches for <I>word</I> according tothe <I>option</I>s, which may be any option accepted by the<B>complete</B> builtin with the exception of <B>-p</B> and <B>-r</B>, and writethe matches to the standard output.When using the <B>-F</B> or <B>-C</B> options, the various shell variablesset by the programmable completion facilities, while available, will nothave useful values.<P>The matches will be generated in the same way as if the programmablecompletion code had generated them directly from a completion specificationwith the same flags.If <I>word</I> is specified, only those completions matching <I>word</I>will be displayed.<P>The return value is true unless an invalid option is supplied, or nomatches were generated.<DT><B>complete</B> [<B>-abcdefgjksuv</B>] [<B>-o</B> <I>comp-option</I>] [<B>-DEI</B>] [<B>-A</B> <I>action</I>] [<B>-G</B> <I>globpat</I>] [<B>-W</B> <I>wordlist</I>]<DD><BR> [<B>-F</B> <I>function</I>] [<B>-C</B> <I>command</I>] [<B>-X</B> <I>filterpat</I>] [<B>-P</B> <I>prefix</I>] [<B>-S</B> <I>suffix</I>] <I>name</I> [<I>name ...</I>] <DT><B>complete</B> <B>-pr</B> [<B>-DEI</B>] [<I>name</I> ...]<DD> Specify how arguments to each <I>name</I> should be completed.If the <B>-p</B> option is supplied, or if no options are supplied,existing completion specifications are printed in a way that allowsthem to be reused as input.The <B>-r</B> option removes a completion specification foreach <I>name</I>, or, if no <I>name</I>s are supplied, allcompletion specifications.The <B>-D</B> option indicates that other supplied options and actions shouldapply to the ``default'' command completion; that is, completion attemptedon a command for which no completion has previously been defined.The <B>-E</B> option indicates that other supplied options and actions shouldapply to ``empty'' command completion; that is, completion attempted on ablank line.The <B>-I</B> option indicates that other supplied options and actions shouldapply to completion on the initial non-assignment word on the line, or aftera command delimiter such as <B>;</B> or <B>|</B>, which is usually commandname completion.If multiple options are supplied, the <B>-D</B> option takes precedenceover <B>-E</B>, and both take precedence over <B>-I</B>.If any of <B>-D</B>, <B>-E</B>, or <B>-I</B> are supplied, any other<I>name</I> arguments are ignored; these completions only apply to the casespecified by the option.<P>The process of applying these completion specifications when word completionis attempted is described above under <B>Programmable Completion</B>.<P>Other options, if specified, have the following meanings.The arguments to the <B>-G</B>, <B>-W</B>, and <B>-X</B> options(and, if necessary, the <B>-P</B> and <B>-S</B> options)should be quoted to protect them from expansion before the<B>complete</B> builtin is invoked.<DL COMPACT><DT><DD> <DL COMPACT><DT><B>-o</B> <I>comp-option</I><DD>The <I>comp-option</I> controls several aspects of the compspec's behaviorbeyond the simple generation of completions.<I>comp-option</I> may be one of:<DL COMPACT><DT><DD><DL COMPACT><DT><B>bashdefault</B> <DD>Perform the rest of the default <B>bash</B> completions if the compspecgenerates no matches.<DT><B>default</B> <DD>Use readline's default filename completion if the compspec generatesno matches.<DT><B>dirnames</B> <DD>Perform directory name completion if the compspec generates no matches.<DT><B>filenames</B> <DD>Tell readline that the compspec generates filenames, so it can perform anyfilename-specific processing (like adding a slash to directory names,quoting special characters, or suppressing trailing spaces).Intended to be used with shell functions.<DT><B>noquote</B> <DD>Tell readline not to quote the completed words if they are filenames(quoting filenames is the default).<DT><B>nosort</B> <DD>Tell readline not to sort the list of possible completions alphabetically.<DT><B>nospace</B> <DD>Tell readline not to append a space (the default) to words completed atthe end of the line.<DT><B>plusdirs</B> <DD>After any matches defined by the compspec are generated,directory name completion is attempted and anymatches are added to the results of the other actions.</DL></DL> <DT><B>-A</B> <I>action</I><DD>The <I>action</I> may be one of the following to generate a list of possiblecompletions:<DL COMPACT><DT><DD><DL COMPACT><DT><B>alias</B> <DD>Alias names.  May also be specified as <B>-a</B>.<DT><B>arrayvar</B> <DD>Array variable names.<DT><B>binding</B> <DD><B>Readline</B> key binding names.<DT><B>builtin</B> <DD>Names of shell builtin commands.  May also be specified as <B>-b</B>.<DT><B>command</B> <DD>Command names.  May also be specified as <B>-c</B>.<DT><B>directory</B> <DD>Directory names.  May also be specified as <B>-d</B>.<DT><B>disabled</B> <DD>Names of disabled shell builtins.<DT><B>enabled</B> <DD>Names of enabled shell builtins.<DT><B>export</B> <DD>Names of exported shell variables.  May also be specified as <B>-e</B>.<DT><B>file</B> <DD>File names.  May also be specified as <B>-f</B>.<DT><B>function</B> <DD>Names of shell functions.<DT><B>group</B> <DD>Group names.  May also be specified as <B>-g</B>.<DT><B>helptopic</B> <DD>Help topics as accepted by the <B>help</B> builtin.<DT><B>hostname</B> <DD>Hostnames, as taken from the file specified by the<FONT SIZE=-1><B>HOSTFILE</B> </FONT>shell variable.<DT><B>job</B> <DD>Job names, if job control is active.  May also be specified as <B>-j</B>.<DT><B>keyword</B> <DD>Shell reserved words.  May also be specified as <B>-k</B>.<DT><B>running</B> <DD>Names of running jobs, if job control is active.<DT><B>service</B> <DD>Service names.  May also be specified as <B>-s</B>.<DT><B>setopt</B> <DD>Valid arguments for the <B>-o</B> option to the <B>set</B> builtin.<DT><B>shopt</B> <DD>Shell option names as accepted by the <B>shopt</B> builtin.<DT><B>signal</B> <DD>Signal names.<DT><B>stopped</B> <DD>Names of stopped jobs, if job control is active.<DT><B>user</B> <DD>User names.  May also be specified as <B>-u</B>.<DT><B>variable</B> <DD>Names of all shell variables.  May also be specified as <B>-v</B>.</DL></DL> <DT><B>-C</B> <I>command</I><DD><I>command</I> is executed in a subshell environment, and its output isused as the possible completions.Arguments are passed as with the <B>-F</B> option.<DT><B>-F</B> <I>function</I><DD>The shell function <I>function</I> is executed in the current shellenvironment.When the function is executed,the first argument (<B>$1</B>) is the name of the command whose arguments arebeing completed,the second argument (<B>$2</B>) is the word being completed,and the third argument (<B>$3</B>) is the word preceding the word beingcompleted on the current command line.When it finishes, the possible completions are retrieved from the valueof the<FONT SIZE=-1><B>COMPREPLY</B> </FONT>array variable.<DT><B>-G</B> <I>globpat</I><DD>The pathname expansion pattern <I>globpat</I> is expanded to generatethe possible completions.<DT><B>-P</B> <I>prefix</I><DD><I>prefix</I> is added at the beginning of each possible completionafter all other options have been applied.<DT><B>-S</B> <I>suffix</I><DD><I>suffix</I> is appended to each possible completionafter all other options have been applied.<DT><B>-W</B> <I>wordlist</I><DD>The <I>wordlist</I> is split using the characters in the<FONT SIZE=-1><B>IFS</B> </FONT>special variable as delimiters, and each resultant word is expanded.Shell quoting is honored within <I>wordlist</I>,in order to provide amechanism for the words to contain shell metacharacters or charactersin the value of<FONT SIZE=-1><B>IFS</B>. </FONT>The possible completions are the members of the resultant list whichmatch the word being completed.<DT><B>-X</B> <I>filterpat</I><DD><I>filterpat</I> is a pattern as used for pathname expansion.It is applied to the list of possible completions generated by thepreceding options and arguments, and each completion matching<I>filterpat</I> is removed from the list.A leading <B>!</B> in <I>filterpat</I> negates the pattern; in thiscase, any completion not matching <I>filterpat</I> is removed. </DL><P> The return value is true unless an invalid option is supplied, an optionother than <B>-p</B> or <B>-r</B> is supplied without a <I>name</I>argument, an attempt is made to remove a completion specification fora <I>name</I> for which no specification exists, oran error occurs adding a completion specification.</DL> <DT><B>compopt</B> [<B>-o</B> <I>option</I>] [<B>-DEI</B>] [<B>+o</B> <I>option</I>] [<I>name</I>]<DD>Modify completion options for each <I>name</I> according to the<I>option</I>s, or for thecurrently-executing completion if no <I>name</I>s are supplied.If no <I>option</I>s are given, display the completion options for each<I>name</I> or the current completion.The possible values of <I>option</I> are those valid for the <B>complete</B>builtin described above.The <B>-D</B> option indicates that other supplied options shouldapply to the ``default'' command completion; that is, completion attemptedon a command for which no completion has previously been defined.The <B>-E</B> option indicates that other supplied options shouldapply to ``empty'' command completion; that is, completion attempted on ablank line.The <B>-I</B> option indicates that other supplied options shouldapply to completion on the initial non-assignment word on the line,or after a command delimiter such as <B>;</B> or <B>|</B>, which is usuallycommand name completion.<P>The return value is true unless an invalid option is supplied, an attemptis made to modify the options for a <I>name</I> for which no completionspecification exists, or an output error occurs.<DT><B>continue</B> [<I>n</I>]<DD>Resume the next iteration of the enclosing<B>for</B>, <B>while</B>, <B>until</B>, or<B>select</B> loop.If<I>n</I> is specified, resume at the <I>n</I>th enclosing loop.<I>n</I> must be >= 1.  If<I>n</I> is greater than the number of enclosing loops, the last enclosing loop(the ``top-level'' loop) is resumed.The return value is 0 unless <I>n</I> is not greater than or equal to 1.<DT><B>declare</B> [<B>-aAfFgiIlnrtux</B>] [<B>-p</B>] [<I>name</I>[=<I>value</I>] ...]<DD> <DT><B>typeset</B> [<B>-aAfFgiIlnrtux</B>] [<B>-p</B>] [<I>name</I>[=<I>value</I>] ...]<DD> Declare variables and/or give them attributes.If no <I>name</I>s are given then display the values of variables.The<B>-p</B> option will display the attributes and values of each<I>name</I>. When<B>-p</B> is used with <I>name</I> arguments, additional options,other than <B>-f</B> and <B>-F</B>, are ignored.When<B>-p</B> is supplied without <I>name</I> arguments, it will display the attributesand values of all variables having the attributes specified by theadditional options.If no other options are supplied with <B>-p</B>, <B>declare</B> will displaythe attributes and values of all shell variables.  The <B>-f</B> optionwill restrict the display to shell functions.The<B>-F</B> option inhibits the display of function definitions; only thefunction name and attributes are printed.If the <B>extdebug</B> shell option is enabled using <B>shopt</B>,the source file name and line number where each <I>name</I>is defined are displayed as well.  The<B>-F</B> option implies<B>-f</B>. The<B>-g</B> option forces variables to be created or modified at the global scope,even when <B>declare</B> is executed in a shell function.It is ignored in all other cases.The<B>-I</B> option causes local variables to inherit the attributes(except the <I>nameref</I> attribute) and value of any existing variable with the same<I>name</I> at a surrounding scope.If there is no existing variable, the local variable is initially unset.The following options canbe used to restrict output to variables with the specified attribute orto give variables attributes:<DL COMPACT><DT><DD> <DL COMPACT><DT><B>-a</B> <DD>Each <I>name</I> is an indexed array variable (see<B>Arrays</B>  above).<DT><B>-A</B> <DD>Each <I>name</I> is an associative array variable (see<B>Arrays</B>  above).<DT><B>-f</B> <DD>Use function names only.<DT><B>-i</B> <DD>The variable is treated as an integer; arithmetic evaluation (see<FONT SIZE=-1><B>ARITHMETIC EVALUATION</B> </FONT> above)is performed when the variable is assigned a value.<DT><B>-l</B> <DD>When the variable is assigned a value, all upper-case characters areconverted to lower-case.The upper-case attribute is disabled.<DT><B>-n</B> <DD>Give each <I>name</I> the <I>nameref</I> attribute, makingit a name reference to another variable.That other variable is defined by the value of <I>name</I>.All references, assignments, and attribute modificationsto <I>name</I>, except those using or changing the<B>-n</B> attribute itself, are performed on the variable referenced by<I>name</I>'s value.The nameref attribute cannot be applied to array variables.<DT><B>-r</B> <DD>Make <I>name</I>s readonly.  These names cannot then be assigned valuesby subsequent assignment statements or unset.<DT><B>-t</B> <DD>Give each <I>name</I> the <I>trace</I> attribute.Traced functions inherit the <B>DEBUG</B> and <B>RETURN</B> traps fromthe calling shell.The trace attribute has no special meaning for variables.<DT><B>-u</B> <DD>When the variable is assigned a value, all lower-case characters areconverted to upper-case.The lower-case attribute is disabled.<DT><B>-x</B> <DD>Mark <I>name</I>s for export to subsequent commands via the environment. </DL><P> Using `+' instead of `-'turns off the attribute instead,with the exceptions that <B>+a</B> and <B>+A</B>may not be used to destroy array variables and <B>+r</B> will notremove the readonly attribute.When used in a function,<B>declare</B> and<B>typeset</B> make each<I>name</I> local, as with the<B>local</B> command,unless the <B>-g</B> option is supplied.If a variable name is followed by =<I>value</I>, the value ofthe variable is set to <I>value</I>.When using <B>-a</B> or <B>-A</B> and the compound assignment syntax tocreate array variables, additional attributes do not take effect untilsubsequent assignments.The return value is 0 unless an invalid option is encountered,an attempt is made to define a function using <TT>-f foo=bar</TT>,an attempt is made to assign a value to a readonly variable,an attempt is made to assign a value to an array variable withoutusing the compound assignment syntax (see<B>Arrays</B>  above),one of the <I>names</I> is not a valid shell variable name,an attempt is made to turn off readonly status for a readonly variable,an attempt is made to turn off array status for an array variable,or an attempt is made to display a non-existent function with <B>-f</B>.</DL> <DT><B>dirs [-clpv</B>] [+<I>n</I>] [-<I>n</I>] <DD>Without options, displays the list of currently remembered directories.The default display is on a single line with directory names separatedby spaces.Directories are added to the list with the<B>pushd</B> command; the<B>popd</B> command removes entries from the list.The current directory is always the first directory in the stack.<DL COMPACT><DT><DD> <DL COMPACT><DT><B>-c</B> <DD>Clears the directory stack by deleting all of the entries.<DT><B>-l</B> <DD>Produces a listing using full pathnames;the default listing format uses a tilde to denote the home directory.<DT><B>-p</B> <DD>Print the directory stack with one entry per line.<DT><B>-v</B> <DD>Print the directory stack with one entry per line,prefixing each entry with its index in the stack.<DT><B>+</B><I>n</I><DD>Displays the <I>n</I>th entry counting from the left of the listshown by<B>dirs</B> when invoked without options, starting with zero.<DT><B>-</B><I>n</I><DD>Displays the <I>n</I>th entry counting from the right of the listshown by<B>dirs</B> when invoked without options, starting with zero. </DL><P> The return value is 0 unless aninvalid option is supplied or <I>n</I> indexes beyond the endof the directory stack.</DL> <DT><B>disown</B> [<B>-ar</B>] [<B>-h</B>] [<I>jobspec</I> ... | <I>pid</I> ... ]<DD>Without options, remove each<I>jobspec</I> from the table of active jobs.If<I>jobspec</I> is not present, and neither the <B>-a</B> nor the <B>-r</B> optionis supplied, the <I>current job</I> is used.If the <B>-h</B> option is given, each<I>jobspec</I> is not removed from the table, but is marked so that<FONT SIZE=-1><B>SIGHUP</B> </FONT>is not sent to the job if the shell receives a<FONT SIZE=-1><B>SIGHUP</B>. </FONT>If no<I>jobspec</I> is supplied, the<B>-a</B> option means to remove or mark all jobs; the<B>-r</B> option without a<I>jobspec</I> argument restricts operation to running jobs.The return value is 0 unless a<I>jobspec</I> does not specify a valid job.<DT><B>echo</B> [<B>-neE</B>] [<I>arg</I> ...]<DD>Output the <I>arg</I>s, separated by spaces, followed by a newline.The return status is 0 unless a write error occurs.If <B>-n</B> is specified, the trailing newline issuppressed.  If the <B>-e</B> option is given, interpretation ofthe following backslash-escaped characters is enabled.  The<B>-E</B> option disables the interpretation of these escape characters,even on systems where they are interpreted by default.The <B>xpg_echo</B> shell option may be used todynamically determine whether or not <B>echo</B> expands theseescape characters by default.<B>echo</B> does not interpret <B>--</B> to mean the end of options.<B>echo</B> interprets the following escape sequences:<DL COMPACT><DT><DD> <DL COMPACT><DT><B>\a</B> <DD>alert (bell)<DT><B>\b</B> <DD>backspace<DT><B>\c</B> <DD>suppress further output<DT><B>\e</B> <DD><DT><B>\E</B> <DD>an escape character<DT><B>\f</B> <DD>form feed<DT><B>\n</B> <DD>new line<DT><B>\r</B> <DD>carriage return<DT><B>\t</B> <DD>horizontal tab<DT><B>\v</B> <DD>vertical tab<DT><B>\\</B> <DD>backslash<DT><B>\0</B><I>nnn</I> <DD>the eight-bit character whose value is the octal value <I>nnn</I>(zero to three octal digits)<DT><B>\x</B><I>HH</I> <DD>the eight-bit character whose value is the hexadecimal value <I>HH</I>(one or two hex digits)<DT><B>\u</B><I>HHHH</I> <DD>the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value<I>HHHH</I> (one to four hex digits)<DT><B>\U</B><I>HHHHHHHH</I> <DD>the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value<I>HHHHHHHH</I> (one to eight hex digits) </DL></DL> <DT><B>enable</B> [<B>-a</B>] [<B>-dnps</B>] [<B>-f</B> <I>filename</I>] [<I>name</I> ...]<DD>Enable and disable builtin shell commands.Disabling a builtin allows a disk command which has the same nameas a shell builtin to be executed without specifying a full pathname,even though the shell normally searches for builtins before disk commands.If <B>-n</B> is used, each <I>name</I>is disabled; otherwise,<I>names</I> are enabled.  For example, to use the<B>test</B> binary found via the<FONT SIZE=-1><B>PATH</B> </FONT>instead of the shell builtin version, run<TT>enable -n test</TT>. The<B>-f</B> option means to load the new builtin command<I>name</I> from shared object<I>filename</I>, on systems that support dynamic loading.Bash will use the value of the <B>BASH_LOADABLES_PATH</B> variable as acolon-separated list of directories in which to search for <I>filename</I>.The default is system-dependent.The<B>-d</B> option will delete a builtin previously loaded with<B>-f</B>. If no <I>name</I> arguments are given, or if the<B>-p</B> option is supplied, a list of shell builtins is printed.With no other option arguments, the list consists of all enabledshell builtins.If <B>-n</B> is supplied, only disabled builtins are printed.If <B>-a</B> is supplied, the list printed includes all builtins, with anindication of whether or not each is enabled.If <B>-s</B> is supplied, the output is restricted to the POSIX<I>special</I> builtins.If no options are supplied and a <I>name</I> is not a shell builtin,<B>enable</B> will attempt to load <I>name</I> from a shared object named<I>name</I>, as if the command were<TT>enable -f</TT> <I>name name</I> . The return value is 0 unless a<I>name</I> is not a shell builtin or there is an error loading a new builtinfrom a shared object.<DT><B>eval</B> [<I>arg</I> ...]<DD>The <I>arg</I>s are read and concatenated together into a singlecommand.  This command is then read and executed by the shell, andits exit status is returned as the value of<B>eval</B>. If there are no<I>args</I>, or only null arguments,<B>eval</B> returns 0.<DT><B>exec</B> [<B>-cl</B>] [<B>-a</B> <I>name</I>] [<I>command</I> [<I>arguments</I>]]<DD>If<I>command</I> is specified, it replaces the shell.No new process is created.  The<I>arguments</I> become the arguments to <I>command</I>.If the<B>-l</B> option is supplied,the shell places a dash at the beginning of the zeroth argument passed to<I>command</I>. This is what<I>login</I>(1) does.  The<B>-c</B> option causes<I>command</I> to be executed with an empty environment.  If<B>-a</B> is supplied, the shell passes<I>name</I> as the zeroth argument to the executed command.If<I>command</I> cannot be executed for some reason, a non-interactive shell exits,unless the<B>execfail</B> shell optionis enabled.  In that case, it returns failure.An interactive shell returns failure if the file cannot be executed.A subshell exits unconditionally if <B>exec</B> fails.If<I>command</I> is not specified, any redirections take effect in the current shell,and the return status is 0.  If there is a redirection error, thereturn status is 1.<DT><B>exit</B> [<I>n</I>]<DD>Cause the shell to exitwith a status of <I>n</I>.  If<I>n</I> is omitted, the exit statusis that of the last command executed.A trap on<FONT SIZE=-1><B>EXIT</B> </FONT>is executed before the shell terminates.<DT><B>export</B> [<B>-fn</B>] [<I>name</I>[=<I>word</I>]] ...<DD> <DT><B>export -p</B> <DD> The supplied<I>names</I> are marked for automatic export to the environment ofsubsequently executed commands.  If the<B>-f</B> option is given, the<I>names</I> refer to functions.If no<I>names</I> are given, or if the<B>-p</B> option is supplied, a listof names of all exported variables is printed.The<B>-n</B> option causes the export property to be removed from each<I>name</I>.If a variable name is followed by =<I>word</I>, the value ofthe variable is set to <I>word</I>.<B>export</B> returns an exit status of 0 unless an invalid option isencountered,one of the <I>names</I> is not a valid shell variable name, or<B>-f</B> is supplied with a<I>name</I> that is not a function.<DT><B>fc</B> [<B>-e</B> <I>ename</I>] [<B>-lnr</B>] [<I>first</I>] [<I>last</I>]<DD> <DT><B>fc</B> <B>-s</B> [<I>pat</I>=<I>rep</I>] [<I>cmd</I>]<DD> The first form selects a range of commands from<I>first</I> to<I>last</I> from the history list and displays or edits and re-executes them.<I>First</I> and<I>last</I> may be specified as a string (to locate the last command beginningwith that string) or as a number (an index into the history list,where a negative number is used as an offset from the currentcommand number).When listing, a <I>first</I> or <I>last</I> of0 is equivalent to -1 and -0 is equivalent to the currentcommand (usually the <B>fc</B> command); otherwise 0 is equivalent to -1and -0 is invalid.If<I>last</I> is not specified, it is set tothe current command for listing (so that <TT>fc -l -10</TT>prints the last 10 commands) and to<I>first</I> otherwise.If<I>first</I> is not specified, it is set to the previouscommand for editing and -16 for listing.<P>The<B>-n</B> option suppressesthe command numbers when listing.  The<B>-r</B> option reverses the order ofthe commands.  If the<B>-l</B> option is given,the commands are listed onstandard output.  Otherwise, the editor given by<I>ename</I> is invokedon a file containing those commands.  If<I>ename</I> is not given, thevalue of the<FONT SIZE=-1><B>FCEDIT</B> </FONT>variable is used, andthe value of<FONT SIZE=-1><B>EDITOR</B> </FONT>if<FONT SIZE=-1><B>FCEDIT</B> </FONT>is not set.  If neither variable is set, <I>vi</I> is used.  When editing is complete, the edited commands areechoed and executed.<P>In the second form, <I>command</I> is re-executed after each instanceof <I>pat</I> is replaced by <I>rep</I>.<I>Command</I> is interpreted the same as <I>first</I> above.A useful alias to use with this is <TT>r='fc -s'</TT>,so that typing <TT>r cc</TT>runs the last command beginning with <TT>cc</TT>and typing <TT>r</TT>re-executes the last command.<P>If the first form is used, the return value is 0 unless an invalidoption is encountered or<I>first</I> or<I>last</I> specify history lines out of range.If the<B>-e</B> option is supplied, the return value is the value of the lastcommand executed or failure if an error occurs with the temporaryfile of commands.  If the second form is used, the return statusis that of the command re-executed, unless<I>cmd</I> does not specify a valid history line, in which case<B>fc</B> returns failure.<DT><B>fg</B> [<I>jobspec</I>]<DD>Resume<I>jobspec</I> in the foreground, and make it the current job.If<I>jobspec</I> is not present, the shell's notion of the <I>current job</I> is used.The return value is that of the command placed into the foreground,or failure if run when job control is disabled or, when run withjob control enabled, if<I>jobspec</I> does not specify a valid job or<I>jobspec</I> specifies a job that was started without job control.<DT><B>getopts</B> <I>optstring</I> <I>name</I> [<I>arg ...</I>]<DD><B>getopts</B> is used by shell procedures to parse positional parameters.<I>optstring</I> contains the option characters to be recognized; if a characteris followed by a colon, the option is expected to have anargument, which should be separated from it by white space.The colon and question mark characters may not be used asoption characters.Each time it is invoked,<B>getopts</B> places the next option in the shell variable<I>name</I>, initializing<I>name</I> if it does not exist,and the index of the next argument to be processed into thevariable<FONT SIZE=-1><B>OPTIND</B>. </FONT><FONT SIZE=-1><B>OPTIND</B> </FONT>is initialized to 1 each time the shell or a shell scriptis invoked.  When an option requires an argument,<B>getopts</B> places that argument into the variable<FONT SIZE=-1><B>OPTARG</B>. </FONT>The shell does not reset<FONT SIZE=-1><B>OPTIND</B> </FONT>automatically; it must be manually reset between multiplecalls to<B>getopts</B> within the same shell invocation if a new set of parametersis to be used.<P>When the end of options is encountered, <B>getopts</B> exits with areturn value greater than zero.<FONT SIZE=-1><B>OPTIND</B> </FONT>is set to the index of the first non-option argument,and <I>name</I> is set to ?.<P><B>getopts</B> normally parses the positional parameters, but if more arguments aresupplied as<I>arg</I> values,<B>getopts</B> parses those instead.<P><B>getopts</B> can report errors in two ways.  If the first character of<I>optstring</I> is a colon,<I>silent</I> error reporting is used.  In normal operation, diagnostic messagesare printed when invalid options or missing option arguments areencountered.If the variable<FONT SIZE=-1><B>OPTERR</B> </FONT>is set to 0, no error messages will be displayed, even if the firstcharacter of<I>optstring</I> is not a colon.<P>If an invalid option is seen,<B>getopts</B> places ? into<I>name</I> and, if not silent,prints an error message and unsets<FONT SIZE=-1><B>OPTARG</B>. </FONT>If<B>getopts</B> is silent,the option character found is placed in<FONT SIZE=-1><B>OPTARG</B> </FONT>and no diagnostic message is printed.<P>If a required argument is not found, and<B>getopts</B> is not silent,a question mark (<B>?</B>) is placed in<I>name</I>, <FONT SIZE=-1><B>OPTARG</B> </FONT>is unset, and a diagnostic message is printed.If<B>getopts</B> is silent, then a colon (<B>:</B>) is placed in<I>name</I> and<FONT SIZE=-1><B>OPTARG</B> </FONT>is set to the option character found.<P><B>getopts</B> returns true if an option, specified or unspecified, is found.It returns false if the end of options is encountered or anerror occurs.<DT><B>hash</B> [<B>-lr</B>] [<B>-p</B> <I>filename</I>] [<B>-dt</B>] [<I>name</I>]<DD>Each time <B>hash</B> is invoked,the full pathname of the command<I>name</I> is determined by searchingthe directories in<B>$PATH</B> and remembered.  Any previously-remembered pathname is discarded.If the<B>-p</B> option is supplied, no path search is performed, and<I>filename</I> is used as the full filename of the command.The<B>-r</B> option causes the shell to forget allremembered locations.The<B>-d</B> option causes the shell to forget the remembered location of each <I>name</I>.If the<B>-t</B> option is supplied, the full pathname to which each <I>name</I> correspondsis printed.  If multiple <I>name</I> arguments are supplied with <B>-t</B>,the <I>name</I> is printed before the hashed full pathname.The<B>-l</B> option causes output to be displayed in a format that may be reused as input.If no arguments are given, or if only <B>-l</B> is supplied,information about remembered commands is printed.The return status is true unless a<I>name</I> is not found or an invalid option is supplied.<DT><B>help</B> [<B>-dms</B>] [<I>pattern</I>]<DD>Display helpful information about builtin commands.  If<I>pattern</I> is specified,<B>help</B> gives detailed help on all commands matching<I>pattern</I>; otherwise help for all the builtins and shell control structuresis printed.<DL COMPACT><DT><DD> <DL COMPACT><DT><B>-d</B> <DD>Display a short description of each <I>pattern</I><DT><B>-m</B> <DD>Display the description of each <I>pattern</I> in a manpage-like format<DT><B>-s</B> <DD>Display only a short usage synopsis for each <I>pattern</I> </DL><P> The return status is 0 unless no command matches<I>pattern</I>. </DL> <DT><B>history [</B><I>n</I>]<DD> <DT><B>history</B> <B>-c</B><DD><DT><B>history -d</B> <I>offset</I><DD><DT><B>history -d</B> <I>start</I>-<I>end</I><DD><DT><B>history</B> <B>-anrw</B> [<I>filename</I>]<DD><DT><B>history</B> <B>-p</B> <I>arg</I> [<I>arg ...</I>]<DD><DT><B>history</B> <B>-s</B> <I>arg</I> [<I>arg ...</I>]<DD> With no options, display the commandhistory list with line numbers.  Lines listedwith a<B>*</B> have been modified.  An argument of<I>n</I> lists only the last<I>n</I> lines.If the shell variable<FONT SIZE=-1><B>HISTTIMEFORMAT</B> </FONT>is set and not null,it is used as a format string for <I>strftime</I>(3) to displaythe time stamp associated with each displayed history entry.No intervening blank is printed between the formatted time stampand the history line.If <I>filename</I> is supplied, it is used as thename of the history file; if not, the value of<FONT SIZE=-1><B>HISTFILE</B> </FONT>is used.  Options, if supplied, have the following meanings:<DL COMPACT><DT><DD> <DL COMPACT><DT><B>-c</B> <DD>Clear the history list by deleting all the entries.<DT><B>-d</B> <I>offset</I><DD>Delete the history entry at position <I>offset</I>.If <I>offset</I> is negative, it is interpreted as relative to one greaterthan the last history position, so negative indices count back from theend of the history, and an index of -1 refers to the current<B>history -d</B> command.<DT><B>-d</B> <I>start</I>-<I>end</I><DD>Delete the range of history entries between positions <I>start</I> and<I>end</I>, inclusive.Positive and negative values for <I>start</I> and <I>end</I>are interpreted as described above.<DT><B>-a</B> <DD>Append the ``new'' history lines to the history file.These are history lines entered since the beginning of the current<B>bash</B> session, but not already appended to the history file.<DT><B>-n</B> <DD>Read the history lines not already read from the historyfile into the current history list.  These are linesappended to the history file since the beginning of thecurrent <B>bash</B> session.<DT><B>-r</B> <DD>Read the contents of the history fileand append them to the current history list.<DT><B>-w</B> <DD>Write the current history list to the history file, overwriting thehistory file's contents.<DT><B>-p</B> <DD>Perform history substitution on the following <I>args</I> and displaythe result on the standard output.Does not store the results in the history list.Each <I>arg</I> must be quoted to disable normal history expansion.<DT><B>-s</B> <DD>Store the<I>args</I> in the history list as a single entry.  The last command in thehistory list is removed before the<I>args</I> are added. </DL><P> If the<FONT SIZE=-1><B>HISTTIMEFORMAT</B> </FONT>variable is set, the time stamp informationassociated with each history entry is written to the history file,marked with the history comment character.When the history file is read, lines beginning with the historycomment character followed immediately by a digit are interpretedas timestamps for the following history entry.The return value is 0 unless an invalid option is encountered, anerror occurs while reading or writing the history file, an invalid<I>offset</I> or range is supplied as an argument to <B>-d</B>, or thehistory expansion supplied as an argument to <B>-p</B> fails.</DL> <DT><B>jobs</B> [<B>-lnprs</B>] [ <I>jobspec</I> ... ]<DD> <DT><B>jobs</B> <B>-x</B> <I>command</I> [ <I>args</I> ... ]<DD> The first form lists the active jobs.  The options have the followingmeanings:<DL COMPACT><DT><DD> <DL COMPACT><DT><B>-l</B> <DD>List process IDsin addition to the normal information.<DT><B>-n</B> <DD>Display information only about jobs that have changed status sincethe user was last notified of their status.<DT><B>-p</B> <DD>List only the process ID of the job's process groupleader.<DT><B>-r</B> <DD>Display only running jobs.<DT><B>-s</B> <DD>Display only stopped jobs. </DL><P> If<I>jobspec</I> is given, output is restricted to information about that job.The return status is 0 unless an invalid option is encounteredor an invalid<I>jobspec</I> is supplied.<P> If the<B>-x</B> option is supplied,<B>jobs</B> replaces any<I>jobspec</I> found in<I>command</I> or<I>args</I> with the corresponding process group ID, and executes<I>command</I> passing it<I>args</I>, returning its exit status.</DL> <DT><B>kill</B> [<B>-s</B> <I>sigspec</I> | <B>-n</B> <I>signum</I> | <B>-</B><I>sigspec</I>] [<I>pid</I> | <I>jobspec</I>] ...<DD> <DT><B>kill</B> <B>-l</B>|<B>-L</B> [<I>sigspec</I> | <I>exit_status</I>]<DD> Send the signal named by<I>sigspec</I> or<I>signum</I> to the processes named by<I>pid</I> or<I>jobspec</I>. <I>sigspec</I> is either a case-insensitive signal name such as<FONT SIZE=-1><B>SIGKILL</B> </FONT>(with or without the<FONT SIZE=-1><B>SIG</B> </FONT>prefix) or a signal number;<I>signum</I> is a signal number.If<I>sigspec</I> is not present, then<FONT SIZE=-1><B>SIGTERM</B> </FONT>is assumed.An argument of<B>-l</B> lists the signal names.If any arguments are supplied when<B>-l</B> is given, the names of the signals corresponding to the arguments arelisted, and the return status is 0.The <I>exit_status</I> argument to<B>-l</B> is a number specifying either a signal number or the exit status ofa process terminated by a signal.The<B>-L</B> option is equivalent to <B>-l</B>.<B>kill</B> returns true if at least one signal was successfully sent, or falseif an error occurs or an invalid option is encountered.<DT><B>let</B> <I>arg</I> [<I>arg</I> ...]<DD>Each<I>arg</I> is an arithmetic expression to be evaluated (see<FONT SIZE=-1><B>ARITHMETIC EVALUATION</B> </FONT> above).If the last<I>arg</I> evaluates to 0,<B>let</B> returns 1; 0 is returned otherwise.<DT><B>local</B> [<I>option</I>] [<I>name</I>[=<I>value</I>] ... | - ]<DD>For each argument, a local variable named<I>name</I> is created, and assigned<I>value</I>. The <I>option</I> can be any of the options accepted by <B>declare</B>.When<B>local</B> is used within a function, it causes the variable<I>name</I> to have a visible scope restricted to that function and its children.If <I>name</I> is -, the set of shell options is made local to the functionin which <B>local</B> is invoked: shell options changed using the<B>set</B> builtin inside the function are restored to their original valueswhen the function returns.The restore is effected as if a series of <B>set</B> commands were executedto restore the values that were in place before the function.With no operands,<B>local</B> writes a list of local variables to the standard output.  It isan error to use<B>local</B> when not within a function.  The return status is 0 unless<B>local</B> is used outside a function, an invalid<I>name</I> is supplied, or<I>name</I> is a readonly variable.<DT><B>logout</B> <DD>Exit a login shell.<DT><B>mapfile</B> [<B>-d</B> <I>delim</I>] [<B>-n</B> <I>count</I>] [<B>-O</B> <I>origin</I>] [<B>-s</B> <I>count</I>] [<B>-t</B>] [<B>-u</B> <I>fd</I>] [<B>-C</B> <I>callback</I>] [<B>-c</B> <I>quantum</I>] [<I>array</I>]<DD> <DT><B>readarray</B> [<B>-d</B> <I>delim</I>] [<B>-n</B> <I>count</I>] [<B>-O</B> <I>origin</I>] [<B>-s</B> <I>count</I>] [<B>-t</B>] [<B>-u</B> <I>fd</I>] [<B>-C</B> <I>callback</I>] [<B>-c</B> <I>quantum</I>] [<I>array</I>]<DD> Read lines from the standard input into the indexed array variable<I>array</I>, or from file descriptor<I>fd</I> if the<B>-u</B> option is supplied.The variable<FONT SIZE=-1><B>MAPFILE</B> </FONT>is the default <I>array</I>.Options, if supplied, have the following meanings:<DL COMPACT><DT><DD> <DL COMPACT><DT><B>-d</B> <DD>The first character of <I>delim</I> is used to terminate each input line,rather than newline.If <I>delim</I> is the empty string, <B>mapfile</B> will terminate a linewhen it reads a NUL character.<DT><B>-n</B> <DD>Copy at most<I>count</I> lines.  If <I>count</I> is 0, all lines are copied.<DT><B>-O</B> <DD>Begin assigning to<I>array</I> at index<I>origin</I>. The default index is 0.<DT><B>-s</B> <DD>Discard the first <I>count</I> lines read.<DT><B>-t</B> <DD>Remove a trailing <I>delim</I> (default newline) from each line read.<DT><B>-u</B> <DD>Read lines from file descriptor <I>fd</I> instead of the standard input.<DT><B>-C</B> <DD>Evaluate<I>callback</I> each time <I>quantum</I> lines are read.  The <B>-c</B> option specifies<I>quantum</I>. <DT><B>-c</B> <DD>Specify the number of lines read between each call to<I>callback</I>.  </DL><P> If<B>-C</B> is specified without<B>-c</B>, the default quantum is 5000.When <I>callback</I> is evaluated, it is supplied the index of the nextarray element to be assigned and the line to be assigned to that elementas additional arguments.<I>callback</I> is evaluated after the line is read but before thearray element is assigned.<P> If not supplied with an explicit origin, <B>mapfile</B> will clear <I>array</I>before assigning to it.<P> <B>mapfile</B> returns successfully unless an invalid option or optionargument is supplied, <I>array</I> is invalid or unassignable, or if<I>array</I> is not an indexed array.</DL> <DT><B>popd</B> [-<B>n</B>] [+<I>n</I>] [-<I>n</I>]<DD>Removes entries from the directory stack.The elements are numbered from 0 starting at the first directorylisted by <B>dirs</B>.With no arguments, <B>popd</B>removes the top directory from the stack, andchanges to the new top directory.Arguments, if supplied, have the following meanings:<DL COMPACT><DT><DD> <DL COMPACT><DT><B>-n</B> <DD>Suppresses the normal change of directory when removing directoriesfrom the stack, so that only the stack is manipulated.<DT><B>+</B><I>n</I><DD>Removes the <I>n</I>th entry counting from the left of the listshown by<B>dirs</B>, starting with zero, from the stack.For example: <TT>popd +0</TT>removes the first directory, <TT>popd +1</TT>the second.<DT><B>-</B><I>n</I><DD>Removes the <I>n</I>th entry counting from the right of the listshown by<B>dirs</B>, starting with zero.  For example: <TT>popd -0</TT>removes the last directory, <TT>popd -1</TT>the next to last. </DL><P> If the top element of the directory stack is modified, andthe <I>-n</I> option was not supplied, <B>popd</B> uses the <B>cd</B>builtin to change to the directory at the top of the stack.If the <B>cd</B> fails, <B>popd</B> returns a non-zero value.<P> Otherwise,<B>popd</B> returns false if an invalid option is encountered, the directory stackis empty, or a non-existent directory stack entry is specified.<P> If the<B>popd</B> command is successful,bash runs<B>dirs</B> to show the final contents of the directory stack,and the return status is 0.</DL> <DT><B>printf</B> [<B>-v</B> <I>var</I>] <I>format</I> [<I>arguments</I>]<DD>Write the formatted <I>arguments</I> to the standard output under thecontrol of the <I>format</I>.The <B>-v</B> option causes the output to be assigned to the variable<I>var</I> rather than being printed to the standard output.<P>The <I>format</I> is a character string which contains three types of objects:plain characters, which are simply copied to standard output, characterescape sequences, which are converted and copied to the standard output, andformat specifications, each of which causes printing of the next successive<I>argument</I>.In addition to the standard <I>printf</I>(1) format specifications,<B>printf</B> interprets the following extensions:<DL COMPACT><DT><DD> <DL COMPACT><DT><B>%b</B> <DD>causes<B>printf</B> to expand backslash escape sequences in the corresponding<I>argument</I>in the same way as <B>echo -e</B>.<DT><B>%q</B> <DD>causes <B>printf</B> to output the corresponding<I>argument</I> in a format that can be reused as shell input.<DT><B>%Q</B> <DD>like <B>%q</B>, but applies any supplied precision to the <I>argument</I>before quoting it.<DT><B>%(</B><I>datefmt</I>)T <DD>causes <B>printf</B> to output the date-time string resulting from using<I>datefmt</I> as a format string for <I>strftime</I>(3).The corresponding <I>argument</I> is an integer representing the number ofseconds since the epoch.Two special argument values may be used: -1 represents the currenttime, and -2 represents the time the shell was invoked.If no argument is specified, conversion behaves as if -1 had been given.This is an exception to the usual <B>printf</B> behavior. </DL><P> The %b, %q, and %T directives all use the field width and precisionarguments from the format specification and write that many bytes from(or use that wide a field for) the expanded argument, which usuallycontains more characters than the original.<P> Arguments to non-string format specifiers are treated as C constants,except that a leading plus or minus sign is allowed, and if the leadingcharacter is a single or double quote, the value is the ASCII value ofthe following character.<P> The <I>format</I> is reused as necessary to consume all of the <I>arguments</I>.If the <I>format</I> requires more <I>arguments</I> than are supplied, theextra format specifications behave as if a zero value or null string, asappropriate, had been supplied.The return value is zero on success, non-zero on failure.</DL> <DT><B>pushd</B> [<B>-n</B>] [+<I>n</I>] [-<I>n</I>]<DD> <DT><B>pushd</B> [<B>-n</B>] [<I>dir</I>]<DD> Adds a directory to the top of the directory stack, or rotatesthe stack, making the new top of the stack the current workingdirectory.With no arguments, <B>pushd</B> exchanges the top two elements ofthe directory stack.Arguments, if supplied, have the following meanings:<DL COMPACT><DT><DD> <DL COMPACT><DT><B>-n</B> <DD>Suppresses the normal change of directory when rotating oradding directories to the stack, so that only the stack is manipulated.<DT><B>+</B><I>n</I><DD>Rotates the stack so that the <I>n</I>th directory(counting from the left of the list shown by<B>dirs</B>, starting with zero)is at the top.<DT><B>-</B><I>n</I><DD>Rotates the stack so that the <I>n</I>th directory(counting from the right of the list shown by<B>dirs</B>, starting with zero) is at the top.<DT><I>dir</I> <DD>Adds<I>dir</I> to the directory stack at the top </DL><P> After the stack has been modified, if the <B>-n</B> option was notsupplied, <B>pushd</B> uses the <B>cd</B> builtin to change to thedirectory at the top of the stack.If the <B>cd</B> fails, <B>pushd</B> returns a non-zero value.<P> Otherwise, if no arguments are supplied,<B>pushd</B> returns 0 unless the directory stack is empty.When rotating the directory stack,<B>pushd</B> returns 0 unless the directory stack is empty ora non-existent directory stack element is specified.<P> If the<B>pushd</B> command is successful,bash runs<B>dirs</B> to show the final contents of the directory stack.</DL> <DT><B>pwd</B> [<B>-LP</B>]<DD>Print the absolute pathname of the current working directory.The pathname printed contains no symbolic links if the<B>-P</B> option is supplied or the<B>-o physical</B> option to the<B>set</B> builtin command is enabled.If the<B>-L</B> option is used, the pathname printed may contain symbolic links.The return status is 0 unless an error occurs whilereading the name of the current directory or aninvalid option is supplied.<DT><B>read</B> [<B>-ers</B>] [<B>-a</B> <I>aname</I>] [<B>-d</B> <I>delim</I>] [<B>-i</B> <I>text</I>] [<B>-n</B> <I>nchars</I>] [<B>-N</B> <I>nchars</I>] [<B>-p</B> <I>prompt</I>] [<B>-t</B> <I>timeout</I>] [<B>-u</B> <I>fd</I>] [<I>name</I> ...]<DD>One line is read from the standard input, or from the file descriptor<I>fd</I> supplied as an argument to the <B>-u</B> option,split into words as described aboveunder <B>Word Splitting</B>,and the first wordis assigned to the first<I>name</I>, the second word to the second<I>name</I>, and so on.If there are more words than names, the remaining words and theirintervening delimiters are assigned to the last<I>name</I>. If there are fewer words read from the input stream than names,the remaining names are assigned empty values.The characters in<FONT SIZE=-1><B>IFS</B> </FONT>are used to split the line into words using the same rules the shelluses for expansion (described aboveunder <B>Word Splitting</B>).The backslash character (<B>\</B>) may be used to remove any specialmeaning for the next character read and for line continuation.Options, if supplied, have the following meanings:<DL COMPACT><DT><DD> <DL COMPACT><DT><B>-a </B><I>aname</I> <DD>The words are assigned to sequential indicesof the array variable<I>aname</I>, starting at 0.<I>aname</I> is unset before any new values are assigned.Other <I>name</I> arguments are ignored.<DT><B>-d </B><I>delim</I> <DD>The first character of <I>delim</I> is used to terminate the input line,rather than newline.If <I>delim</I> is the empty string, <B>read</B> will terminate a linewhen it reads a NUL character.<DT><B>-e</B> <DD>If the standard inputis coming from a terminal,<B>readline</B> (see<FONT SIZE=-1><B>READLINE</B> </FONT> above)is used to obtain the line.Readline uses the current (or default, if line editing was not previouslyactive) editing settings, but uses readline's default filename completion.<DT><B>-i </B><I>text</I> <DD>If<B>readline</B> is being used to read the line, <I>text</I> is placed into the editingbuffer before editing begins.<DT><B>-n </B><I>nchars</I> <DD><B>read</B> returns after reading <I>nchars</I> characters rather thanwaiting for a complete line of input, but honors a delimiter if fewerthan <I>nchars</I> characters are read before the delimiter.<DT><B>-N </B><I>nchars</I> <DD><B>read</B> returns after reading exactly <I>nchars</I> characters ratherthan waiting for a complete line of input, unless EOF is encountered or<B>read</B> times out.Delimiter characters encountered in the input arenot treated specially and do not cause <B>read</B> to return until<I>nchars</I> characters are read.The result is not split on the characters in <B>IFS</B>; the intent isthat the variable is assigned exactly the characters read(with the exception of backslash; see the <B>-r</B> option below).<DT><B>-p </B><I>prompt</I> <DD>Display <I>prompt</I> on standard error, without atrailing newline, before attempting to read any input.  The promptis displayed only if input is coming from a terminal.<DT><B>-r</B> <DD>Backslash does not act as an escape character.The backslash is considered to be part of the line.In particular, a backslash-newline pair may not then be used as a linecontinuation.<DT><B>-s</B> <DD>Silent mode.  If input is coming from a terminal, characters arenot echoed.<DT><B>-t </B><I>timeout</I> <DD>Cause <B>read</B> to time out and return failure if a complete line ofinput (or a specified number of characters)is not read within <I>timeout</I> seconds.<I>timeout</I> may be a decimal number with a fractional portion followingthe decimal point.This option is only effective if <B>read</B> is reading input from aterminal, pipe, or other special file; it has no effect when readingfrom regular files.If <B>read</B> times out, <B>read</B> saves any partial input read intothe specified variable <I>name</I>.If <I>timeout</I> is 0, <B>read</B> returns immediately, without trying toread any data.The exit status is 0 if input is available on the specified file descriptor,or the read will return EOF,non-zero otherwise.The exit status is greater than 128 if the timeout is exceeded.<DT><B>-u </B><I>fd</I> <DD>Read input from file descriptor <I>fd</I>. </DL><P> If no<I>names</I> are supplied, the line read,without the ending delimiter but otherwise unmodified,is assigned to the variable<FONT SIZE=-1><B>REPLY</B>. </FONT>The exit status is zero, unless end-of-file is encountered, <B>read</B>times out (in which case the status is greater than 128),a variable assignment error (such as assigning to a readonly variable) occurs,or an invalid file descriptor is supplied as the argument to <B>-u</B>.</DL> <DT><B>readonly</B> [<B>-aAf</B>] [<B>-p</B>] [<I>name</I>[=<I>word</I>] ...]<DD> The given<I>names</I> are marked readonly; the values of these<I>names</I> may not be changed by subsequent assignment.If the<B>-f</B> option is supplied, the functions corresponding to the<I>names</I> are somarked.The<B>-a</B> option restricts the variables to indexed arrays; the<B>-A</B> option restricts the variables to associative arrays.If both options are supplied,<B>-A</B> takes precedence.If no<I>name</I> arguments are given, or if the<B>-p</B> option is supplied, a list of all readonly names is printed.The other options may be used to restrict the output to a subset ofthe set of readonly names.The<B>-p</B> option causes output to be displayed in a format thatmay be reused as input.If a variable name is followed by =<I>word</I>, the value ofthe variable is set to <I>word</I>.The return status is 0 unless an invalid option is encountered,one of the<I>names</I> is not a valid shell variable name, or<B>-f</B> is supplied with a<I>name</I> that is not a function.<DT><B>return</B> [<I>n</I>]<DD>Causes a function to stop executing and return the value specified by<I>n</I> to its caller.If<I>n</I> is omitted, the return status is that of the last commandexecuted in the function body.If <B>return</B> is executed by a trap handler, the last command used todetermine the status is the last command executed before the trap handler.If <B>return</B> is executed during a <B>DEBUG</B> trap, the last commandused to determine the status is the last command executed by the traphandler before <B>return</B> was invoked.If<B>return</B> is used outside a function,but during execution of a script by the<B>.</B> (<B>source</B>) command, it causes the shell to stop executingthat script and return either<I>n</I> or the exit status of the last command executed within thescript as the exit status of the script.If <I>n</I> is supplied, the return value is its least significant8 bits.The return status is non-zero if<B>return</B> is supplied a non-numeric argument, oris used outside afunction and not during execution of a script by <B>.</B> or <B>source</B>.Any command associated with the <B>RETURN</B> trap is executedbefore execution resumes after the function or script.<DT><B>set</B> [<B>-abefhkmnptuvxBCEHPT</B>] [<B>-o</B> <I>option-name</I>] [<B>--</B>] [<B>-</B>] [<I>arg</I> ...]<DD> <DT><B>set</B> [<B>+abefhkmnptuvxBCEHPT</B>] [<B>+o</B> <I>option-name</I>] [<B>--</B>] [<B>-</B>] [<I>arg</I> ...]<DD> Without options, display the name and value of each shell variablein a format that can be reused as inputfor setting or resetting the currently-set variables.Read-only variables cannot be reset.In <I>posix mode</I>, only shell variables are listed.The output is sorted according to the current locale.When options are specified, they set or unset shell attributes.Any arguments remaining after option processing are treatedas values for the positional parameters and are assigned, in order, to<B>$1</B>, <B>$2</B>, <B>...</B> <B>$</B><I>n</I>. Options, if specified, have the following meanings:<DL COMPACT><DT><DD> <DL COMPACT><DT><B>-a</B> <DD>Each variable or function that is created or modified is given theexport attribute and marked for export to the environment ofsubsequent commands.<DT><B>-b</B> <DD>Report the status of terminated background jobsimmediately, rather than before the next primary prompt.  This iseffective only when job control is enabled.<DT><B>-e</B> <DD>Exit immediately if a<I>pipeline</I> (which may consist of a single <I>simple command</I>),a <I>list</I>,or a <I>compound command</I>(see<FONT SIZE=-1><B>SHELL GRAMMAR</B> </FONT> above),exits with a non-zero status.The shell does not exit if thecommand that fails is part of the command list immediately following a<B>while</B> or<B>until</B> keyword,part of the test following the<B>if</B> or<B>elif</B> reserved words, part of any command executed in a<B>&amp;&amp;</B> or<B>||</B> list except the command following the final <B>&amp;&amp;</B> or <B>||</B>,any command in a pipeline but the last,or if the command's return value isbeing inverted with<B>!</B>. If a compound command other than a subshellreturns a non-zero status because a command failedwhile <B>-e</B> was being ignored, the shell does not exit.A trap on <B>ERR</B>, if set, is executed before the shell exits.This option applies to the shell environment and each subshell environmentseparately (see<FONT SIZE=-1><B>COMMAND EXECUTION ENVIRONMENT</B> </FONT> above),and may causesubshells to exit before executing all the commands in the subshell.<P>  If a compound command or shell function executes in a contextwhere <B>-e</B> is being ignored,none of the commands executed within the compound command or function bodywill be affected by the <B>-e</B> setting, even if <B>-e</B> is setand a command returns a failure status.If a compound command or shell function sets <B>-e</B> while executing ina context where <B>-e</B> is ignored, that setting will not have anyeffect until the compound command or the command containing the functioncall completes.<DT><B>-f</B> <DD>Disable pathname expansion.<DT><B>-h</B> <DD>Remember the location of commands as they are looked up for execution.This is enabled by default.<DT><B>-k</B> <DD>All arguments in the form of assignment statementsare placed in the environment for a command, not justthose that precede the command name.<DT><B>-m</B> <DD>Monitor mode.  Job control is enabled.  This option is onby default for interactive shells on systems that supportit (see<FONT SIZE=-1><B>JOB CONTROL</B> </FONT> above).All processes run in a separate process group.When a background job completes, the shell prints a linecontaining its exit status.<DT><B>-n</B> <DD>Read commands but do not execute them.This may be used to check a shell script for syntax errors.This is ignored by interactive shells.<DT><B>-o </B><I>option-name</I> <DD>The <I>option-name</I> can be one of the following:<DL COMPACT><DT><DD><DL COMPACT><DT><B>allexport</B> <DD>Same as<B>-a</B>. <DT><B>braceexpand</B> <DD>Same as<B>-B</B>. <DT><B>emacs</B> <DD>Use an emacs-style command line editing interface.  This is enabledby default when the shell is interactive, unless the shell is startedwith the<B>--noediting</B> option.This also affects the editing interface used for <B>read -e</B>.<DT><B>errexit</B> <DD>Same as<B>-e</B>. <DT><B>errtrace</B> <DD>Same as<B>-E</B>. <DT><B>functrace</B> <DD>Same as<B>-T</B>. <DT><B>hashall</B> <DD>Same as<B>-h</B>. <DT><B>histexpand</B> <DD>Same as<B>-H</B>. <DT><B>history</B> <DD>Enable command history, as described aboveunder<FONT SIZE=-1><B>HISTORY</B>. </FONT>This option is on by default in interactive shells.<DT><B>ignoreeof</B> <DD>The effect is as if the shell command<TT>IGNOREEOF=10</TT> had been executed(see<B>Shell Variables</B>  above).<DT><B>keyword</B> <DD>Same as<B>-k</B>. <DT><B>monitor</B> <DD>Same as<B>-m</B>. <DT><B>noclobber</B> <DD>Same as<B>-C</B>. <DT><B>noexec</B> <DD>Same as<B>-n</B>. <DT><B>noglob</B> <DD>Same as<B>-f</B>. <DT><B>nolog</B> <DD>Currently ignored.<DT><B>notify</B> <DD>Same as<B>-b</B>. <DT><B>nounset</B> <DD>Same as<B>-u</B>. <DT><B>onecmd</B> <DD>Same as<B>-t</B>. <DT><B>physical</B> <DD>Same as<B>-P</B>. <DT><B>pipefail</B> <DD>If set, the return value of a pipeline is the value of the last(rightmost) command to exit with a non-zero status, or zero if allcommands in the pipeline exit successfully.This option is disabled by default.<DT><B>posix</B> <DD>Change the behavior of<B>bash</B> where the default operation differsfrom the POSIX standard to match the standard (<I>posix mode</I>).See<FONT SIZE=-1><B>SEE ALSO</B> </FONT> belowfor a reference to a document that details how posix mode affectsbash's behavior.<DT><B>privileged</B> <DD>Same as<B>-p</B>. <DT><B>verbose</B> <DD>Same as<B>-v</B>. <DT><B>vi</B> <DD>Use a vi-style command line editing interface.This also affects the editing interface used for <B>read -e</B>.<DT><B>xtrace</B> <DD>Same as<B>-x</B>. <P></DL><P> If<B>-o</B> is supplied with no <I>option-name</I>, the values of the current options areprinted.If<B>+o</B> is supplied with no <I>option-name</I>, a series of<B>set</B> commands to recreate the current option settings is displayed onthe standard output.</DL> <DT><B>-p</B> <DD>Turn on<I>privileged</I> mode.  In this mode, the<FONT SIZE=-1><B>$ENV</B> </FONT>and<FONT SIZE=-1><B>$BASH_ENV</B> </FONT>files are not processed, shell functions are not inherited from theenvironment, and the<FONT SIZE=-1><B>SHELLOPTS</B>, </FONT><FONT SIZE=-1><B>BASHOPTS</B>, </FONT><FONT SIZE=-1><B>CDPATH</B>, </FONT>and<FONT SIZE=-1><B>GLOBIGNORE</B> </FONT>variables, if they appear in the environment, are ignored.If the shell is started with the effective user (group) id not equal to thereal user (group) id, and the <B>-p</B> option is not supplied, these actionsare taken and the effective user id is set to the real user id.If the <B>-p</B> option is supplied at startup, the effective user id isnot reset.Turning this option off causes the effective userand group ids to be set to the real user and group ids.<DT><B>-r</B> <DD>Enable restricted shell mode.This option cannot be unset once it has been set.<DT><B>-t</B> <DD>Exit after reading and executing one command.<DT><B>-u</B> <DD>Treat unset variables and parameters other than the specialparameters &quot;@&quot; and &quot;*&quot;,or array variables subscripted with &quot;@&quot; or &quot;*&quot;,as an error when performingparameter expansion.  If expansion is attempted on anunset variable or parameter, the shell prints an error message, and,if not interactive, exits with a non-zero status.<DT><B>-v</B> <DD>Print shell input lines as they are read.<DT><B>-x</B> <DD>After expanding each <I>simple command</I>,<B>for</B> command, <B>case</B> command, <B>select</B> command, orarithmetic <B>for</B> command, display the expanded value of<FONT SIZE=-1><B>PS4</B>, </FONT>followed by the command and its expanded argumentsor associated word list.<DT><B>-B</B> <DD>The shell performs brace expansion (see<B>Brace Expansion</B>  above).This is on by default.<DT><B>-C</B> <DD>If set,<B>bash</B> does not overwrite an existing file with the<B>&gt;</B>, <B>&gt;&amp;</B>, and<B>&lt;&gt;</B> redirection operators.  This may be overridden whencreating output files by using the redirection operator<B>&gt;|</B> instead of<B>&gt;</B>. <DT><B>-E</B> <DD>If set, any trap on <B>ERR</B> is inherited by shell functions, commandsubstitutions, and commands executed in a subshell environment.The <B>ERR</B> trap is normally not inherited in such cases.<DT><B>-H</B> <DD>Enable<B>!</B> style history substitution.  This option is on bydefault when the shell is interactive.<DT><B>-P</B> <DD>If set, the shell does not resolve symbolic links when executingcommands such as<B>cd</B> that change the current working directory.  It uses thephysical directory structure instead.  By default,<B>bash</B> follows the logical chain of directories when performing commandswhich change the current directory.<DT><B>-T</B> <DD>If set, any traps on <B>DEBUG</B> and <B>RETURN</B> are inherited by shellfunctions, command substitutions, and commands executed in asubshell environment.The <B>DEBUG</B> and <B>RETURN</B> traps are normally not inheritedin such cases.<DT><B>--</B> <DD>If no arguments follow this option, then the positional parameters areunset.  Otherwise, the positional parameters are set to the<I>arg</I>s, even if some of them begin with a<B>-</B>. <DT><B>-</B> <DD>Signal the end of options, cause all remaining <I>arg</I>s to beassigned to the positional parameters.  The<B>-x</B> and<B>-v</B> options are turned off.If there are no <I>arg</I>s,the positional parameters remain unchanged. </DL><P> The options are off by default unless otherwise noted.Using + rather than - causes these options to be turned off.The options can also be specified as arguments to an invocation ofthe shell.The current set of options may be found in<B>$-</B>. The return status is always true unless an invalid option is encountered.</DL> <DT><B>shift</B> [<I>n</I>]<DD>The positional parameters from <I>n</I>+1 ... are renamed to<B>$1</B> <B>....</B> Parameters represented by the numbers <B>$#</B>down to <B>$#</B>-<I>n</I>+1 are unset.<I>n</I> must be a non-negative number less than or equal to <B>$#</B>.If<I>n</I> is 0, no parameters are changed.If<I>n</I> is not given, it is assumed to be 1.If<I>n</I> is greater than <B>$#</B>, the positional parameters are not changed.The return status is greater than zero if<I>n</I> is greater than<B>$#</B> or less than zero; otherwise 0.<DT><B>shopt</B> [<B>-pqsu</B>] [<B>-o</B>] [<I>optname</I> ...]<DD>Toggle the values of settings controlling optional shell behavior.The settings can be either those listed below, or, if the<B>-o</B> option is used, those available with the<B>-o</B> option to the <B>set</B> builtin command.With no options, or with the<B>-p</B> option, a list of all settable options is displayed, withan indication of whether or not each is set;if <I>optnames</I> are supplied, the output is restricted to those options.The <B>-p</B> option causes output to be displayed in a form thatmay be reused as input.Other options have the following meanings:<DL COMPACT><DT><DD> <DL COMPACT><DT><B>-s</B> <DD>Enable (set) each <I>optname</I>.<DT><B>-u</B> <DD>Disable (unset) each <I>optname</I>.<DT><B>-q</B> <DD>Suppresses normal output (quiet mode); the return status indicateswhether the <I>optname</I> is set or unset.If multiple <I>optname</I> arguments are given with<B>-q</B>, the return status is zero if all <I>optnames</I> are enabled; non-zerootherwise.<DT><B>-o</B> <DD>Restricts the values of <I>optname</I> to be those defined for the<B>-o</B> option to the<B>set</B> builtin. </DL><P> If either<B>-s</B> or<B>-u</B> is used with no <I>optname</I> arguments,<B>shopt</B> shows only those options which are set or unset, respectively.Unless otherwise noted, the <B>shopt</B> options are disabled (unset)by default.<P> The return status when listing options is zero if all <I>optnames</I>are enabled, non-zero otherwise.  When setting or unsetting options,the return status is zero unless an <I>optname</I> is not a valid shelloption.<P> The list of <B>shopt</B> options is:<P>   <DL COMPACT><DT><B>assoc_expand_once</B> <DD>If set, the shell suppresses multiple evaluation of associative arraysubscripts during arithmetic expression evaluation, while executingbuiltins that can perform variable assignments,and while executing builtins that perform array dereferencing.<DT><B>autocd</B> <DD>If set, a command name that is the name of a directory is executed as ifit were the argument to the <B>cd</B> command.This option is only used by interactive shells.<DT><B>cdable_vars</B> <DD>If set, an argument to the<B>cd</B> builtin command thatis not a directory is assumed to be the name of a variable whosevalue is the directory to change to.<DT><B>cdspell</B> <DD>If set, minor errors in the spelling of a directory component in a<B>cd</B> command will be corrected.The errors checked for are transposed characters,a missing character, and one character too many.If a correction is found, the corrected filename is printed,and the command proceeds.This option is only used by interactive shells.<DT><B>checkhash</B> <DD>If set, <B>bash</B> checks that a command found in the hashtable exists before trying to execute it.  If a hashed command nolonger exists, a normal path search is performed.<DT><B>checkjobs</B> <DD>If set, <B>bash</B> lists the status of any stopped and running jobs beforeexiting an interactive shell.  If any jobs are running, this causesthe exit to be deferred until a second exit is attempted without anintervening command (see<FONT SIZE=-1><B>JOB CONTROL</B> </FONT> above).The shell always postpones exiting if any jobs are stopped.<DT><B>checkwinsize</B> <DD>If set, <B>bash</B> checks the window size after each external (non-builtin)command and, if necessary, updates the values of<FONT SIZE=-1><B>LINES</B> </FONT>and<FONT SIZE=-1><B>COLUMNS</B>. </FONT>This option is enabled by default.<DT><B>cmdhist</B> <DD>If set,<B>bash</B> attempts to save all lines of a multiple-linecommand in the same history entry.  This allowseasy re-editing of multi-line commands.This option is enabled by default, but only has an effect if commandhistory is enabled, as described aboveunder<FONT SIZE=-1><B>HISTORY</B>. </FONT> <DT><B>compat31</B> <DD><DT><B>compat32</B> <DD><DT><B>compat40</B> <DD><DT><B>compat41</B> <DD><DT><B>compat42</B> <DD><DT><B>compat43</B> <DD><DT><B>compat44</B> <DD><DT><B>compat50</B> <DD> These control aspects of the shell's compatibility mode(see<FONT SIZE=-1><B>SHELL COMPATIBILITY MODE</B> </FONT> below).<DT><B>complete_fullquote</B> <DD>If set,<B>bash</B> quotes all shell metacharacters in filenames and directory names whenperforming completion.If not set,<B>bash</B> removes metacharacters such as the dollar sign from the set ofcharacters that will be quoted in completed filenameswhen these metacharacters appear in shell variable references in words to becompleted.This means that dollar signs in variable names that expand to directorieswill not be quoted;however, any dollar signs appearing in filenames will not be quoted, either.This is active only when bash is using backslashes to quote completedfilenames.This variable is set by default, which is the default bash behavior inversions through 4.2.<DT><B>direxpand</B> <DD>If set,<B>bash</B> replaces directory names with the results of word expansion when performingfilename completion.  This changes the contents of the readline editingbuffer.If not set,<B>bash</B> attempts to preserve what the user typed.<DT><B>dirspell</B> <DD>If set,<B>bash</B> attempts spelling correction on directory names during word completionif the directory name initially supplied does not exist.<DT><B>dotglob</B> <DD>If set,<B>bash</B> includes filenames beginning with a `.' in the results of pathnameexpansion.The filenames<B>``.''</B> and<B>``..''</B> must always be matched explicitly, even if<B>dotglob</B> is set.<DT><B>execfail</B> <DD>If set, a non-interactive shell will not exit ifit cannot execute the file specified as an argument to the<B>exec</B> builtin command.  An interactive shell does not exit if<B>exec</B> fails.<DT><B>expand_aliases</B> <DD>If set, aliases are expanded as described aboveunder<FONT SIZE=-1><B>ALIASES</B>. </FONT>This option is enabled by default for interactive shells.<DT><B>extdebug</B> <DD>If set at shell invocation,or in a shell startup file,arrange to execute the debugger profilebefore the shell starts, identical to the <B>--debugger</B> option.If set after invocation, behavior intended for use by debuggers is enabled:<DL COMPACT><DT><DD><DL COMPACT><DT><B>1.</B> <DD>The <B>-F</B> option to the <B>declare</B> builtin displays the sourcefile name and line number corresponding to each function name suppliedas an argument.<DT><B>2.</B> <DD>If the command run by the <B>DEBUG</B> trap returns a non-zero value, thenext command is skipped and not executed.<DT><B>3.</B> <DD>If the command run by the <B>DEBUG</B> trap returns a value of 2, and theshell is executing in a subroutine (a shell function or a shell scriptexecuted by the <B>.</B> or <B>source</B> builtins), the shell simulatesa call to <B>return</B>.<DT><B>4.</B> <DD><FONT SIZE=-1><B>BASH_ARGC</B> </FONT>and<FONT SIZE=-1><B>BASH_ARGV</B> </FONT>are updated as described in their descriptions above).<DT><B>5.</B> <DD>Function tracing is enabled: command substitution, shell functions, andsubshells invoked with <B>(</B> <I>command</I> <B>)</B> inherit the<B>DEBUG</B> and <B>RETURN</B> traps.<DT><B>6.</B> <DD>Error tracing is enabled: command substitution, shell functions, andsubshells invoked with <B>(</B> <I>command</I> <B>)</B> inherit the<B>ERR</B> trap.</DL></DL> <DT><B>extglob</B> <DD>If set, the extended pattern matching features described aboveunder<B>Pathname Expansion</B> are enabled.<DT><B>extquote</B> <DD>If set, <B>$</B>aq<I>string</I>aq and <B>$</B>&quot;<I>string</I>&quot; quoting isperformed within <B>${</B><I>parameter</I><B>}</B> expansionsenclosed in double quotes.  This option is enabled by default.<DT><B>failglob</B> <DD>If set, patterns which fail to match filenames during pathname expansionresult in an expansion error.<DT><B>force_fignore</B> <DD>If set, the suffixes specified by the<FONT SIZE=-1><B>FIGNORE</B> </FONT>shell variablecause words to be ignored when performing word completion even ifthe ignored words are the only possible completions.See<FONT SIZE=-1><B>SHELL VARIABLES</B></FONT> abovefor a description of<FONT SIZE=-1><B>FIGNORE</B>. </FONT>This option is enabled by default.<DT><B>globasciiranges</B> <DD>If set, range expressions used in pattern matching bracket expressions (see<FONT SIZE=-1><B>Pattern Matching</B> </FONT> above)behave as if in the traditional C locale when performingcomparisons.  That is, the current locale's collating sequenceis not taken into account, so<B>b</B> will not collate between<B>A</B> and<B>B</B>, and upper-case and lower-case ASCII characters will collate together.<DT><B>globskipdots</B> <DD>If set, pathname expansion will never match the filenames<B>``.''</B> and<B>``..''</B>, even if the pattern begins with a<B>``.''</B>. This option is enabled by default.<DT><B>globstar</B> <DD>If set, the pattern <B>**</B> used in a pathname expansion context willmatch all files and zero or more directories and subdirectories.If the pattern is followed by a <B>/</B>, only directories andsubdirectories match.<DT><B>gnu_errfmt</B> <DD>If set, shell error messages are written in the standard GNU errormessage format.<DT><B>histappend</B> <DD>If set, the history list is appended to the file named by the valueof the<FONT SIZE=-1><B>HISTFILE</B> </FONT>variable when the shell exits, rather than overwriting the file.<DT><B>histreedit</B> <DD>If set, and<B>readline</B> is being used, a user is given the opportunity to re-edit afailed history substitution.<DT><B>histverify</B> <DD>If set, and<B>readline</B> is being used, the results of history substitution are not immediatelypassed to the shell parser.  Instead, the resulting line is loaded intothe <B>readline</B> editing buffer, allowing further modification.<DT><B>hostcomplete</B> <DD>If set, and<B>readline</B> is being used, <B>bash</B> will attempt to perform hostname completion when aword containing a <B>@</B> is being completed (see<B>Completing</B> under<FONT SIZE=-1><B>READLINE</B> </FONT> above).This is enabled by default.<DT><B>huponexit</B> <DD>If set, <B>bash</B> will send<FONT SIZE=-1><B>SIGHUP</B> </FONT>to all jobs when an interactive login shell exits.<DT><B>inherit_errexit</B> <DD>If set, command substitution inherits the value of the <B>errexit</B> option,instead of unsetting it in the subshell environment.This option is enabled when <I>posix mode</I> is enabled.<DT><B>interactive_comments</B> <DD>If set, allow a word beginning with<B>#</B> to cause that word and all remaining characters on thatline to be ignored in an interactive shell (see<FONT SIZE=-1><B>COMMENTS</B> </FONT> above).This option is enabled by default.<DT><B>lastpipe</B> <DD>If set, and job control is not active, the shell runs the last command ofa pipeline not executed in the background in the current shell environment.<DT><B>lithist</B> <DD>If set, and the<B>cmdhist</B> option is enabled, multi-line commands are saved to the history withembedded newlines rather than using semicolon separators where possible.<DT><B>localvar_inherit</B> <DD>If set, local variables inherit the value and attributes of a variable ofthe same name that exists at a previous scope before any new value isassigned.  The nameref attribute is not inherited.<DT><B>localvar_unset</B> <DD>If set, calling <B>unset</B> on local variables in previous function scopesmarks them so subsequent lookups find them unset until that functionreturns. This is identical to the behavior of unsetting local variablesat the current function scope.<DT><B>login_shell</B> <DD>The shell sets this option if it is started as a login shell (see<FONT SIZE=-1><B>INVOCATION</B> </FONT> above).The value may not be changed.<DT><B>mailwarn</B> <DD>If set, and a file that <B>bash</B> is checking for mail has beenaccessed since the last time it was checked, the message ``The mail in<I>mailfile</I> has been read'' is displayed.<DT><B>no_empty_cmd_completion</B> <DD>If set, and<B>readline</B> is being used,<B>bash</B> will not attempt to search the<FONT SIZE=-1><B>PATH</B> </FONT>for possible completions whencompletion is attempted on an empty line.<DT><B>nocaseglob</B> <DD>If set,<B>bash</B> matches filenames in a case-insensitive fashion when performing pathnameexpansion (see<B>Pathname Expansion</B>  above).<DT><B>nocasematch</B> <DD>If set,<B>bash</B> matches patterns in a case-insensitive fashion when performing matchingwhile executing <B>case</B> or <B>[[</B> conditional commands,when performing pattern substitution word expansions,or when filtering possible completions as part of programmable completion.<DT><B>noexpand_translation</B> <DD>If set,<B>bash</B> encloses the translated results of $&quot;...&quot; quoting in single quotesinstead of double quotes.If the string is not translated, this has no effect.<DT><B>nullglob</B> <DD>If set,<B>bash</B> allows patterns which match nofiles (see<B>Pathname Expansion</B>  above)to expand to a null string, rather than themselves.<DT><B>patsub_replacement</B> <DD>If set, <B>bash</B>expands occurrences of <B>&amp;</B> in the replacement string of patternsubstitution to the text matched by the pattern, as describedunder <B>Parameter Expansion</B> above.This option is enabled by default.<DT><B>progcomp</B> <DD>If set, the programmable completion facilities (see<B>Programmable Completion</B> above)are enabled.This option is enabled by default.<DT><B>progcomp_alias</B> <DD>If set, and programmable completion is enabled, <B>bash</B> treats a commandname that doesn't have any completions as a possible alias and attemptsalias expansion. If it has an alias, <B>bash</B> attempts programmablecompletion using the command word resulting from the expanded alias.<DT><B>promptvars</B> <DD>If set, prompt strings undergoparameter expansion, command substitution, arithmeticexpansion, and quote removal after being expanded as described in<FONT SIZE=-1><B>PROMPTING</B> </FONT> above.This option is enabled by default.<DT><B>restricted_shell</B> <DD>The shell sets this option if it is started in restricted mode(see<FONT SIZE=-1><B>RESTRICTED SHELL</B> </FONT> below).The value may not be changed.This is not reset when the startup files are executed, allowingthe startup files to discover whether or not a shell is restricted.<DT><B>shift_verbose</B> <DD>If set, the<B>shift</B> builtin prints an error message when the shift count exceeds thenumber of positional parameters.<DT><B>sourcepath</B> <DD>If set, the<B>.</B> (<B>source</B>) builtin uses the value of<FONT SIZE=-1><B>PATH</B> </FONT>to find the directory containing the file supplied as an argument.This option is enabled by default.<DT><B>varredir_close</B> <DD>If set, the shell automatically closes file descriptors assigned using the<I>{varname}</I> redirection syntax (see<FONT SIZE=-1><B>REDIRECTION</B> </FONT> above)instead of leaving them open when the command completes.<DT><B>xpg_echo</B> <DD>If set, the <B>echo</B> builtin expands backslash-escape sequencesby default.</DL></DL>  <DT><B>suspend</B> [<B>-f</B>]<DD>Suspend the execution of this shell until it receives a<FONT SIZE=-1><B>SIGCONT</B> </FONT>signal.  A login shell,or a shell without job control enabled,cannot be suspended; the<B>-f</B> option can be used to override this and force the suspension.The return status is 0 unless the shell is a login shellor job control is not enabledand<B>-f</B> is not supplied.<DT><B>test</B> <I>expr</I><DD> <DT><B>[</B> <I>expr</I> <B>]</B><DD>Return a status of 0 (true) or 1 (false) depending onthe evaluation of the conditional expression<I>expr</I>. Each operator and operand must be a separate argument.Expressions are composed of the primaries described  aboveunder<FONT SIZE=-1><B>CONDITIONAL EXPRESSIONS</B>. </FONT><B>test</B> does not accept any options, nor does it accept and ignorean argument of <B>--</B> as signifying the end of options.<P>  Expressions may be combined using the following operators, listedin decreasing order of precedence.The evaluation depends on the number of arguments; see below.Operator precedence is used when there are five or more arguments.<DL COMPACT><DT><DD> <DL COMPACT><DT><B>! </B><I>expr</I> <DD>True if<I>expr</I> is false.<DT><B>( </B><I>expr</I> ) <DD>Returns the value of <I>expr</I>.This may be used to override the normal precedence of operators.<DT><I>expr1</I> -<B>a</B> <I>expr2</I><DD>True if both<I>expr1</I> and<I>expr2</I> are true.<DT><I>expr1</I> -<B>o</B> <I>expr2</I><DD>True if either<I>expr1</I> or<I>expr2</I> is true. </DL><P> <B>test</B> and <B>[</B> evaluate conditionalexpressions using a set of rules based on the number of arguments.<P>   <DL COMPACT><DT>0 arguments<DD>The expression is false.<DT>1 argument<DD>The expression is true if and only if the argument is not null.<DT>2 arguments<DD>If the first argument is <B>!</B>, the expression is true if andonly if the second argument is null.If the first argument is one of the unary conditional operators listed aboveunder<FONT SIZE=-1><B>CONDITIONAL EXPRESSIONS</B>, </FONT>the expression is true if the unary test is true.If the first argument is not a valid unary conditional operator, the expressionis false.<DT>3 arguments<DD>The following conditions are applied in the order listed.If the second argument is one of the binary conditional operators listed aboveunder<FONT SIZE=-1><B>CONDITIONAL EXPRESSIONS</B>, </FONT>the result of the expression is the result of the binary test usingthe first and third arguments as operands.The <B>-a</B> and <B>-o</B> operators are considered binary operatorswhen there are three arguments.If the first argument is <B>!</B>, the value is the negation ofthe two-argument test using the second and third arguments.If the first argument is exactly <B>(</B> and the third argument isexactly <B>)</B>, the result is the one-argument test of the secondargument.Otherwise, the expression is false.<DT>4 arguments<DD>The following conditions are applied in the order listed.If the first argument is <B>!</B>, the result is the negation ofthe three-argument expression composed of the remaining arguments.the two-argument test using the second and third arguments.If the first argument is exactly <B>(</B> and the fourth argument isexactly <B>)</B>, the result is the two-argument test of the secondand third arguments.Otherwise, the expression is parsed and evaluated according toprecedence using the rules listed above.<DT>5 or more arguments<DD>The expression is parsed and evaluated according to precedenceusing the rules listed above.<P>  </DL><P> When used with <B>test</B> or <B>[</B>, the <B>&lt;</B> and <B>&gt;</B> operatorssort lexicographically using ASCII ordering.</DL>  <DT><B>times</B> <DD>Print the accumulated user and system times for the shell andfor processes run from the shell.  The return status is 0.<DT><B>trap</B> [<B>-lp</B>] [[<I>arg</I>] <I>sigspec</I> ...]<DD>The command<I>arg</I> is to be read and executed when the shell receivessignal(s)<I>sigspec</I>. If<I>arg</I> is absent (and there is a single <I>sigspec</I>) or<B>-</B>, each specified signal isreset to its original disposition (the value it hadupon entrance to the shell).If<I>arg</I> is the null string the signal specified by each<I>sigspec</I> is ignored by the shell and by the commands it invokes.If<I>arg</I> is not present and<B>-p</B> has been supplied, then the trap commands associated with each<I>sigspec</I> are displayed.If no arguments are supplied or if only<B>-p</B> is given,<B>trap</B> prints the list of commands associated with each signal.The<B>-l</B> option causes the shell to print a list of signal names andtheir corresponding numbers.Each<I>sigspec</I> is eithera signal name defined in &lt;<I>signal.h</I>&gt;, or a signal number.Signal names are case insensitive and the<FONT SIZE=-1><B>SIG</B> </FONT>prefix is optional.<P>  If a<I>sigspec</I> is<FONT SIZE=-1><B>EXIT</B> </FONT>(0) the command<I>arg</I> is executed on exit from the shell.If a<I>sigspec</I> is<FONT SIZE=-1><B>DEBUG</B>, </FONT>the command<I>arg</I> is executed before every <I>simple command</I>, <I>for</I> command,<I>case</I> command, <I>select</I> command, every arithmetic <I>for</I>command, and before the first command executes in a shell function (see<FONT SIZE=-1><B>SHELL GRAMMAR</B> </FONT> above).Refer to the description of the <B>extdebug</B> option to the<B>shopt</B> builtin for details of its effect on the <B>DEBUG</B> trap.If a<I>sigspec</I> is<FONT SIZE=-1><B>RETURN</B>, </FONT>the command<I>arg</I> is executed each time a shell function or a script executed withthe <B>.</B> or <B>source</B> builtins finishes executing.<P>  If a<I>sigspec</I> is<FONT SIZE=-1><B>ERR</B>, </FONT>the command<I>arg</I> is executed whenevera pipeline (which may consist of a single simplecommand), a list, or a compound command returns anon-zero exit status,subject to the following conditions.The<FONT SIZE=-1><B>ERR</B> </FONT>trap is not executed if the failedcommand is part of the command list immediately following a<B>while</B> or<B>until</B> keyword,part of the test in an<I>if</I> statement, part of a command executed in a<B>&amp;&amp;</B> or<B>||</B> list except the command following the final <B>&amp;&amp;</B> or <B>||</B>,any command in a pipeline but the last,or if the command's return value isbeing inverted using<B>!</B>. These are the same conditions obeyed by the <B>errexit</B> (<B>-e</B>) option.<P>  Signals ignored upon entry to the shell cannot be trapped or reset.Trapped signals that are not being ignored are reset to their originalvalues in a subshell or subshell environment when one is created.The return status is false if any<I>sigspec</I> is invalid; otherwise<B>trap</B> returns true.<DT><B>type</B> [<B>-aftpP</B>] <I>name</I> [<I>name</I> ...]<DD>With no options,indicate how each<I>name</I> would be interpreted if used as a command name.If the<B>-t</B> option is used,<B>type</B> prints a string which is one of<I>alias</I>, <I>keyword</I>, <I>function</I>, <I>builtin</I>, or<I>file</I> if<I>name</I> is an alias, shell reserved word, function, builtin, or disk file,respectively.If the<I>name</I> is not found, then nothing is printed, and an exit status of falseis returned.If the<B>-p</B> option is used,<B>type</B> either returns the name of the disk filethat would be executed if<I>name</I> were specified as a command name,or nothing if<TT>type -t name</TT> would not return<I>file</I>. The<B>-P</B> option forces a<FONT SIZE=-1><B>PATH</B> </FONT>search for each <I>name</I>, even if<TT>type -t name</TT> would not return<I>file</I>. If a command is hashed,<B>-p</B> and<B>-P</B> print the hashed value, which is not necessarily the file that appearsfirst in<FONT SIZE=-1><B>PATH</B>. </FONT>If the<B>-a</B> option is used,<B>type</B> prints all of the places that containan executable named<I>name</I>. This includes aliases and functions,if and only if the<B>-p</B> option is not also used.The table of hashed commands is not consultedwhen using<B>-a</B>. The<B>-f</B> option suppresses shell function lookup, as with the <B>command</B> builtin.<B>type</B> returns true if all of the arguments are found, false ifany are not found.<DT><B>ulimit</B> [<B>-HS</B>] <B>-a</B><DD> <DT><B>ulimit</B> [<B>-HS</B>] [<B>-bcdefiklmnpqrstuvxPRT</B> [<I>limit</I>]]<DD> Provides control over the resources available to the shell and toprocesses started by it, on systems that allow such control.The <B>-H</B> and <B>-S</B> options specify that the hard or soft limit isset for the given resource.A hard limit cannot be increased by a non-root user once it is set;a soft limit may be increased up to the value of the hard limit.If neither <B>-H</B> nor <B>-S</B> is specified, both the soft and hardlimits are set.The value of<I>limit</I> can be a number in the unit specified for the resourceor one of the special values<B>hard</B>, <B>soft</B>, or<B>unlimited</B>, which stand for the current hard limit, the current soft limit, andno limit, respectively.If<I>limit</I> is omitted, the current value of the soft limit of the resource isprinted, unless the <B>-H</B> option is given.  When more than oneresource is specified, the limit name and unit, if appropriate,are printed before the value.Other options are interpreted as follows:<DL COMPACT><DT><DD> <DL COMPACT><DT><B>-a</B> <DD>All current limits are reported; no limits are set<DT><B>-b</B> <DD>The maximum socket buffer size<DT><B>-c</B> <DD>The maximum size of core files created<DT><B>-d</B> <DD>The maximum size of a process's data segment<DT><B>-e</B> <DD>The maximum scheduling priority (&quot;nice&quot;)<DT><B>-f</B> <DD>The maximum size of files written by the shell and its children<DT><B>-i</B> <DD>The maximum number of pending signals<DT><B>-k</B> <DD>The maximum number of kqueues that may be allocated<DT><B>-l</B> <DD>The maximum size that may be locked into memory<DT><B>-m</B> <DD>The maximum resident set size (many systems do not honor this limit)<DT><B>-n</B> <DD>The maximum number of open file descriptors (most systems do notallow this value to be set)<DT><B>-p</B> <DD>The pipe size in 512-byte blocks (this may not be set)<DT><B>-q</B> <DD>The maximum number of bytes in POSIX message queues<DT><B>-r</B> <DD>The maximum real-time scheduling priority<DT><B>-s</B> <DD>The maximum stack size<DT><B>-t</B> <DD>The maximum amount of cpu time in seconds<DT><B>-u</B> <DD>The maximum number of processes available to a single user<DT><B>-v</B> <DD>The maximum amount of virtual memory available to the shell and, onsome systems, to its children<DT><B>-x</B> <DD>The maximum number of file locks<DT><B>-P</B> <DD>The maximum number of pseudoterminals<DT><B>-R</B> <DD>The maximum time a real-time process can run before blocking, in microseconds<DT><B>-T</B> <DD>The maximum number of threads </DL><P> If<I>limit</I> is given, and the<B>-a</B> option is not used,<I>limit</I> is the new value of the specified resource.If no option is given, then<B>-f</B> is assumed.  Values are in 1024-byte increments, except for<B>-t</B>, which is in seconds;<B>-R</B>, which is in microseconds;<B>-p</B>, which is in units of 512-byte blocks;<B>-P</B>, <B>-T</B>, <B>-b</B>, <B>-k</B>, <B>-n</B>, and<B>-u</B>, which are unscaled values;and, when in posix mode,<B>-c</B> and<B>-f</B>, which are in 512-byte increments.The return status is 0 unless an invalid option or argument is supplied,or an error occurs while setting a new limit.</DL> <DT><B>umask</B> [<B>-p</B>] [<B>-S</B>] [<I>mode</I>]<DD>The user file-creation mask is set to<I>mode</I>. If<I>mode</I> begins with a digit, itis interpreted as an octal number; otherwiseit is interpreted as a symbolic mode mask similarto that accepted by<I>chmod</I>(1). If<I>mode</I> is omitted, the current value of the mask is printed.The<B>-S</B> option causes the mask to be printed in symbolic form; thedefault output is an octal number.If the<B>-p</B> option is supplied, and<I>mode</I> is omitted, the output is in a form that may be reused as input.The return status is 0 if the mode was successfully changed or ifno <I>mode</I> argument was supplied, and false otherwise.<DT><B>unalias</B> [-<B>a</B>] [<I>name</I> ...]<DD>Remove each <I>name</I> from the list of defined aliases.  If<B>-a</B> is supplied, all alias definitions are removed.  The returnvalue is true unless a supplied<I>name</I> is not a defined alias.<DT><B>unset</B> [-<B>fv</B>] [-<B>n</B>] [<I>name</I> ...]<DD>For each<I>name</I>, remove the corresponding variable or function.If the<B>-v</B> option is given, each<I>name</I> refers to a shell variable, and that variable is removed.Read-only variables may not be unset.If<B>-f</B> is specified, each<I>name</I> refers to a shell function, and the function definitionis removed.If the<B>-n</B> option is supplied, and <I>name</I> is a variable with the <I>nameref</I>attribute, <I>name</I> will be unset rather than the variable itreferences.<B>-n</B> has no effect if the <B>-f</B> option is supplied.If no options are supplied, each <I>name</I> refers to a variable; ifthere is no variable by that name, a function with that name, if any, isunset.Each unset variable or function is removed from the environmentpassed to subsequent commands.If any of<FONT SIZE=-1><B>BASH_ALIASES</B>, </FONT><FONT SIZE=-1><B>BASH_ARGV0</B>, </FONT><FONT SIZE=-1><B>BASH_CMDS</B>, </FONT><FONT SIZE=-1><B>BASH_COMMAND</B>, </FONT><FONT SIZE=-1><B>BASH_SUBSHELL</B>, </FONT><FONT SIZE=-1><B>BASHPID</B>, </FONT><FONT SIZE=-1><B>COMP_WORDBREAKS</B>, </FONT><FONT SIZE=-1><B>DIRSTACK</B>, </FONT><FONT SIZE=-1><B>EPOCHREALTIME</B>, </FONT><FONT SIZE=-1><B>EPOCHSECONDS</B>, </FONT><FONT SIZE=-1><B>FUNCNAME</B>, </FONT><FONT SIZE=-1><B>GROUPS</B>, </FONT><FONT SIZE=-1><B>HISTCMD</B>, </FONT><FONT SIZE=-1><B>LINENO</B>, </FONT><FONT SIZE=-1><B>RANDOM</B>, </FONT><FONT SIZE=-1><B>SECONDS</B>, </FONT>or<FONT SIZE=-1><B>SRANDOM</B> </FONT>are unset, they lose their special properties, even if they aresubsequently reset.  The exit status is true unless a<I>name</I> is readonly or may not be unset.<DT><B>wait</B> [<B>-fn</B>] [-p <I>varname</I>] [<I>id ...</I>]<DD>Wait for each specified child process and return its termination status.Each<I>id</I> may be a processID or a job specification; if a job spec is given, all processesin that job's pipeline are waited for.  If<I>id</I> is not given,<B>wait</B> waits for all running background jobs andthe last-executed process substitution, if its process id is the same as<B>$!</B>,and the return status is zero.If the <B>-n</B> option is supplied,<B>wait</B> waits for a single jobfrom the list of <I>id</I>s or, if no <I>id</I>s are supplied, any job,to complete and returns its exit status.If none of the supplied arguments is a child of the shell, or if no argumentsare supplied and the shell has no unwaited-for children, the exit statusis 127.If the <B>-p</B> option is supplied, the process or job identifier of the jobfor which the exit status is returned is assigned to the variable<I>varname</I> named by the option argument.The variable will be unset initially, before any assignment.This is useful only when the <B>-n</B> option is supplied.Supplying the <B>-f</B> option, when job control is enabled,forces <B>wait</B> to wait for <I>id</I> to terminate before returningits status, instead of returning when it changes status.If<I>id</I> specifies a non-existent process or job, the return status is 127.If <B>wait</B> is interrupted by a signal, the return status will be greaterthan 128, as described under<B>SIGNALS</B>  above.Otherwise, the return status is the exit status of the lastprocess or job waited for.</DL><A NAME="lbDC">&nbsp;</A><H3>SHELL COMPATIBILITY MODE</H3> Bash-4.0 introduced the concept of a <I>shell compatibility level</I>,specified as a set of options to the shopt builtin (<B>compat31</B>, <B>compat32</B>, <B>compat40</B>, <B>compat41</B>, and so on).There is only one currentcompatibility level -- each option is mutually exclusive.The compatibility level is intended to allow users to select behaviorfrom previous versions that is incompatible with newer versionswhile they migrate scripts to use current features andbehavior. It's intended to be a temporary solution.<P> This section does not mention behavior that is standard for a particularversion (e.g., setting <B>compat32</B> means that quoting the rhs of the regexpmatching operator quotes special regexp characters in the word, which isdefault behavior in bash-3.2 and subsequent versions). <P> If a user enables, say, <B>compat32</B>, it may affect the behavior of othercompatibility levels up to and including the current compatibility level.The idea is that each compatibility level controls behavior that changedin that version of <B>bash</B>,but that behavior may have been present in earlier versions.For instance, the change to use locale-based comparisons with the <B>[[</B>command came in bash-4.1, and earlier versions used ASCII-based comparisons,so enabling <B>compat32</B> will enable ASCII-based comparisons as well.That granularity may not be sufficient forall uses, and as a result users should employ compatibility levels carefully.Read the documentation for a particular feature to find out thecurrent behavior.<P> Bash-4.3 introduced a new shell variable:<FONT SIZE=-1><B>BASH_COMPAT</B>. </FONT>The value assignedto this variable (a decimal version number like 4.2, or an integercorresponding to the <B>compat</B><I>NN</I> option, like 42) determines thecompatibility level.<P> Starting with bash-4.4, Bash has begun deprecating older compatibilitylevels.Eventually, the options will be removed in favor of<FONT SIZE=-1><B>BASH_COMPAT</B>. </FONT><P> Bash-5.0 is the final version for which there will be an individual shoptoption for the previous version. Users should use<FONT SIZE=-1><B>BASH_COMPAT</B> </FONT>on bash-5.0 and later versions.<P> The following table describes the behavior changes controlled by eachcompatibility level setting.The <B>compat</B><I>NN</I> tag is used as shorthand for setting thecompatibility levelto <I>NN</I> using one of the following mechanisms.For versions prior to bash-5.0, the compatibility level may be set usingthe corresponding <B>compat</B><I>NN</I> shopt option.For bash-4.3 and later versions, the<FONT SIZE=-1><B>BASH_COMPAT</B> </FONT>variable is preferred,and it is required for bash-5.1 and later versions.<DL COMPACT><DT><B>compat31</B><DD> <DL COMPACT><DT><DD><DL COMPACT><DT>*<DD>quoting the rhs of the <B>[[</B> command's regexp matching operator (=~)has no special effect</DL></DL>  <DT><B>compat32</B><DD> <DL COMPACT><DT><DD><DL COMPACT><DT>*<DD>interrupting a command list such as &quot;a ; b ; c&quot; causes the executionof the next command in the list (in bash-4.0 and later versions,the shell acts as if it received the interrupt, sointerrupting one command in a list aborts the execution of theentire list)</DL></DL>  <DT><B>compat40</B><DD> <DL COMPACT><DT><DD><DL COMPACT><DT>*<DD>the <B>&lt;</B> and <B>&gt;</B> operators to the <B>[[</B> command do notconsider the current locale when comparing strings; they use ASCIIordering.Bash versions prior to bash-4.1 use ASCII collation and<I>strcmp</I>(3); bash-4.1 and later use the current locale's collation sequence and<I>strcoll</I>(3). </DL></DL>  <DT><B>compat41</B><DD> <DL COMPACT><DT><DD><DL COMPACT><DT>*<DD>in <I>posix</I> mode, <B>time</B> may be followed by options and still berecognized as a reserved word (this is POSIX interpretation 267)<DT>*<DD>in <I>posix</I> mode, the parser requires that an even number of singlequotes occur in the <I>word</I> portion of a double-quotedparameter expansion and treats them specially, so that characters withinthe single quotes are considered quoted(this is POSIX interpretation 221)</DL></DL>  <DT><B>compat42</B><DD> <DL COMPACT><DT><DD><DL COMPACT><DT>*<DD>the replacement string in double-quoted pattern substitution does notundergo quote removal, as it does in versions after bash-4.2<DT>*<DD>in posix mode, single quotes are considered special when expandingthe <I>word</I> portion of a double-quoted parameter expansionand can be used to quote a closing brace or other special character(this is part of POSIX interpretation 221);in later versions, single quotesare not special within double-quoted word expansions</DL></DL>  <DT><B>compat43</B><DD> <DL COMPACT><DT><DD><DL COMPACT><DT>*<DD>the shell does not print a warning message if an attempt is made touse a quoted compound assignment as an argument to declare(e.g., declare -a foo=aq(1 2)aq). Later versions warn that this usage isdeprecated<DT>*<DD>word expansion errors are considered non-fatal errors that cause thecurrent command to fail, even in posix mode(the default behavior is to make them fatal errors that cause the shellto exit)<DT>*<DD>when executing a shell function, the loop state (while/until/etc.)is not reset, so <B>break</B> or <B>continue</B> in that function will breakor continue loops in the calling context. Bash-4.4 and later resetthe loop state to prevent this</DL></DL>  <DT><B>compat44</B><DD> <DL COMPACT><DT><DD><DL COMPACT><DT>*<DD>the shell sets up the values used by<FONT SIZE=-1><B>BASH_ARGV</B> </FONT>and<FONT SIZE=-1><B>BASH_ARGC</B> </FONT>so they can expand to the shell's positional parameters even if extendeddebugging mode is not enabled<DT>*<DD>a subshell inherits loops from its parent context, so <B>break</B>or <B>continue</B> will cause the subshell to exit.Bash-5.0 and later reset the loop state to prevent the exit<DT>*<DD>variable assignments preceding builtins like <B>export</B> and <B>readonly</B>that set attributes continue to affect variables with the samename in the calling environment even if the shell is not in posixmode</DL></DL>  <DT><B>compat50</B><DD> <DL COMPACT><DT><DD><DL COMPACT><DT>*<DD>Bash-5.1 changed the way<FONT SIZE=-1><B>$RANDOM</B> </FONT>is generated to introduce slightlymore randomness. If the shell compatibility level is set to 50 orlower, it reverts to the method from bash-5.0 and previous versions,so seeding the random number generator by assigning a value to<FONT SIZE=-1><B>RANDOM</B> </FONT>will produce the same sequence as in bash-5.0<DT>*<DD>If the command hash table is empty, bash versions prior to bash-5.1printed an informational message to that effect, even when producingoutput that can be reused as input. Bash-5.1 suppresses that messagewhen the <B>-l</B> option is supplied.</DL></DL>  <DT><B>compat51</B><DD> <DL COMPACT><DT><DD><DL COMPACT><DT>*<DD>The <B>unset</B> builtin treats attempts to unset array subscripts <B>@</B>and <B>*</B> differently depending on whether the array is indexed orassociative, and differently than in previous versions.</DL></DL>    </DL><A NAME="lbDD">&nbsp;</A><H3>RESTRICTED SHELL</H3>   <P> If<B>bash</B> is started with the name<B>rbash</B>, or the<B>-r</B> option is supplied at invocation,the shell becomes restricted.A restricted shell is used toset up an environment more controlled than the standard shell.It behaves identically to<B>bash</B> with the exception that the following are disallowed or not performed:<DL COMPACT><DT>*<DD>changing directories with <B>cd</B><DT>*<DD>setting or unsetting the values of<FONT SIZE=-1><B>SHELL</B>, </FONT><FONT SIZE=-1><B>PATH</B>, </FONT><FONT SIZE=-1><B>HISTFILE</B>, </FONT><FONT SIZE=-1><B>ENV</B>, </FONT>or<FONT SIZE=-1><B>BASH_ENV</B> </FONT><DT>*<DD>specifying command names containing<B>/</B> <DT>*<DD>specifying a filename containing a<B>/</B> as an argument to the<B>.</B> builtin command<DT>*<DD>specifying a filename containing a slash as an argument to the<B>history</B> builtin command<DT>*<DD>specifying a filename containing a slash as an argument to the<B>-p</B> option to the<B>hash</B> builtin command<DT>*<DD>importing function definitions from the shell environment at startup<DT>*<DD>parsing the value of<FONT SIZE=-1><B>SHELLOPTS</B> </FONT>from the shell environment at startup<DT>*<DD>redirecting output using the &gt;, &gt;|, &lt;&gt;, &gt;&amp;, &amp;&gt;, and &gt;&gt; redirection operators<DT>*<DD>using the<B>exec</B> builtin command to replace the shell with another command<DT>*<DD>adding or deleting builtin commands with the<B>-f</B> and<B>-d</B> options to the<B>enable</B> builtin command<DT>*<DD>using the <B>enable</B> builtin command to enable disabled shell builtins<DT>*<DD>specifying the<B>-p</B> option to the<B>command</B> builtin command<DT>*<DD>turning off restricted mode with<B>set +r</B> or <B>shopt -u restricted_shell</B>.</DL><P> These restrictions are enforced after any startup files are read.<P>   When a command that is found to be a shell script is executed(see<FONT SIZE=-1><B>COMMAND EXECUTION</B> </FONT> above), <B>rbash</B> turns off any restrictions in the shell spawned to execute thescript.  <A NAME="lbDE">&nbsp;</A><H3>SEE ALSO</H3>  <DL COMPACT><DT><I>Bash Reference Manual</I>, Brian Fox and Chet Ramey<DD><DT><I>The Gnu Readline Library</I>, Brian Fox and Chet Ramey<DD><DT><I>The Gnu History Library</I>, Brian Fox and Chet Ramey<DD><DT><I>Portable Operating System Interface (POSIX) Part 2: Shell and Utilities</I>, IEEE --<DD><A HREF="http://pubs.opengroup.org/onlinepubs/9699919799/">http://pubs.opengroup.org/onlinepubs/9699919799/</A><DT><A HREF="http://tiswww.case.edu/~chet/bash/POSIX">http://tiswww.case.edu/~chet/bash/POSIX</A> -- a description of posix mode<DD><DT><I>sh</I>(1), <I>ksh</I>(1), <I>csh</I>(1)<DD><DT><I>emacs</I>(1), <I>vi</I>(1)<DD><DT><I>readline</I>(3)<DD> </DL><A NAME="lbDF">&nbsp;</A><H3>FILES</H3>  <DL COMPACT><DT><A HREF="file:/bin/bash"><I>/bin/bash</I></A> <DD>The <B>bash</B> executable<DT><A HREF="file:/etc/profile"><I>/etc/profile</I></A> <DD>The systemwide initialization file, executed for login shells<DT><A HREF="file:~/.bash_profile"><I>~/.bash_profile</I></A> <DD>The personal initialization file, executed for login shells<DT><A HREF="file:~/.bashrc"><I>~/.bashrc</I></A> <DD>The individual per-interactive-shell startup file<DT><A HREF="file:~/.bash_logout"><I>~/.bash_logout</I></A> <DD>The individual login shell cleanup file, executed when a login shell exits<DT><A HREF="file:~/.bash_history"><I>~/.bash_history</I></A> <DD>The default value of <B>HISTFILE</B>, the file in which bash saves thecommand history<DT><A HREF="file:~/.inputrc"><I>~/.inputrc</I></A> <DD>Individual <I>readline</I> initialization file </DL><A NAME="lbDG">&nbsp;</A><H3>AUTHORS</H3> Brian Fox, Free Software Foundation<BR> <A HREF="mailto:bfox@gnu.org">bfox@gnu.org</A><P> Chet Ramey, Case Western Reserve University<BR> <A HREF="mailto:chet.ramey@case.edu">chet.ramey@case.edu</A><A NAME="lbDH">&nbsp;</A><H3>BUG REPORTS</H3> If you find a bug in<B>bash,</B> you should report it.  But first, you shouldmake sure that it really is a bug, and that it appears in the latestversion of<B>bash</B>. The latest version is always available from<I><A HREF="ftp://ftp.gnu.org/pub/gnu/bash/">ftp://ftp.gnu.org/pub/gnu/bash/</A></I> and<I><A HREF="http://git.savannah.gnu.org/cgit/bash.git/snapshot/bash-master.tar.gz">http://git.savannah.gnu.org/cgit/bash.git/snapshot/bash-master.tar.gz</A></I>.<P> Once you have determined that a bug actually exists, use the<I>bashbug</I> command to submit a bug report.If you have a fix, you are encouraged to mail that as well!Suggestions and `philosophical' bug reports may be mailedto <I><A HREF="mailto:bug-bash@gnu.org">bug-bash@gnu.org</A></I> or posted to the Usenetnewsgroup<A HREF="news:gnu.bash.bug">gnu.bash.bug</A>. <P> ALL bug reports should include:<P>  <DL COMPACT><DT>The version number of <B>bash</B><DD><DT>The hardware and operating system<DD><DT>The compiler used to compile<DD><DT>A description of the bug behaviour<DD><DT>A short script or `recipe' which exercises the bug<DD> </DL><P> <I>bashbug</I> inserts the first three items automatically into the templateit provides for filing a bug report.<P> Comments and bug reports concerningthis manual page should be directed to<I><A HREF="mailto:chet.ramey@case.edu">chet.ramey@case.edu</A></I>. <A NAME="lbDI">&nbsp;</A><H3>BUGS</H3> It's too big and too slow.<P> There are some subtle differences between<B>bash</B> and traditional versions of<B>sh</B>, mostly because of the<FONT SIZE=-1><B>POSIX</B> </FONT>specification.<P> Aliases are confusing in some uses.<P> Shell builtin commands and functions are not stoppable/restartable.<P> Compound commands and command sequences of the form `a ; b ; c'are not handled gracefully when process suspension is attempted.When a process is stopped, the shell immediately executes the nextcommand in the sequence.It suffices to place the sequence of commands betweenparentheses to force it into a subshell, which may be stopped asa unit.<P> Array variables may not (yet) be exported.<P> There may be only one active coprocess at a time.   <HR><TABLE WIDTH=100%><TR><TH ALIGN=LEFT width=33%>GNU Bash 5.2<TH ALIGN=CENTER width=33%>2022 September 19<TH ALIGN=RIGHT width=33%>BASH(1)</TR></TABLE><HR><A NAME="index">&nbsp;</A><H2>Index</H2><DL><DT><A HREF="#lbAB">NAME</A><DD><DT><A HREF="#lbAC">SYNOPSIS</A><DD><DT><A HREF="#lbAD">COPYRIGHT</A><DD><DT><A HREF="#lbAE">DESCRIPTION</A><DD><DT><A HREF="#lbAF">OPTIONS</A><DD><DT><A HREF="#lbAG">ARGUMENTS</A><DD><DT><A HREF="#lbAH">INVOCATION</A><DD><DT><A HREF="#lbAI">DEFINITIONS</A><DD><DT><A HREF="#lbAJ">RESERVED WORDS</A><DD><DT><A HREF="#lbAK">SHELL GRAMMAR</A><DD><DL><DT><A HREF="#lbAL">Simple Commands</A><DD><DT><A HREF="#lbAM">Pipelines</A><DD><DT><A HREF="#lbAN">Lists</A><DD><DT><A HREF="#lbAO">Compound Commands</A><DD><DT><A HREF="#lbAP">Coprocesses</A><DD><DT><A HREF="#lbAQ">Shell Function Definitions</A><DD></DL><DT><A HREF="#lbAR">COMMENTS</A><DD><DT><A HREF="#lbAS">QUOTING</A><DD><DT><A HREF="#lbAT">PARAMETERS</A><DD><DL><DT><A HREF="#lbAU">Positional Parameters</A><DD><DT><A HREF="#lbAV">Special Parameters</A><DD><DT><A HREF="#lbAW">Shell Variables</A><DD><DT><A HREF="#lbAX">Arrays</A><DD></DL><DT><A HREF="#lbAY">EXPANSION</A><DD><DL><DT><A HREF="#lbAZ">Brace Expansion</A><DD><DT><A HREF="#lbBA">Tilde Expansion</A><DD><DT><A HREF="#lbBB">Parameter Expansion</A><DD><DT><A HREF="#lbBC">Command Substitution</A><DD><DT><A HREF="#lbBD">Arithmetic Expansion</A><DD><DT><A HREF="#lbBE">Process Substitution</A><DD><DT><A HREF="#lbBF">Word Splitting</A><DD><DT><A HREF="#lbBG">Pathname Expansion</A><DD><DT><A HREF="#lbBH">Quote Removal</A><DD></DL><DT><A HREF="#lbBI">REDIRECTION</A><DD><DL><DT><A HREF="#lbBJ">Redirecting Input</A><DD><DT><A HREF="#lbBK">Redirecting Output</A><DD><DT><A HREF="#lbBL">Appending Redirected Output</A><DD><DT><A HREF="#lbBM">Redirecting Standard Output and Standard Error</A><DD><DT><A HREF="#lbBN">Appending Standard Output and Standard Error</A><DD><DT><A HREF="#lbBO">Here Documents</A><DD><DT><A HREF="#lbBP">Here Strings</A><DD><DT><A HREF="#lbBQ">Duplicating File Descriptors</A><DD><DT><A HREF="#lbBR">Moving File Descriptors</A><DD><DT><A HREF="#lbBS">Opening File Descriptors for Reading and Writing</A><DD></DL><DT><A HREF="#lbBT">ALIASES</A><DD><DT><A HREF="#lbBU">FUNCTIONS</A><DD><DT><A HREF="#lbBV">ARITHMETIC EVALUATION</A><DD><DT><A HREF="#lbBW">CONDITIONAL EXPRESSIONS</A><DD><DT><A HREF="#lbBX">SIMPLE COMMAND EXPANSION</A><DD><DT><A HREF="#lbBY">COMMAND EXECUTION</A><DD><DT><A HREF="#lbBZ">COMMAND EXECUTION ENVIRONMENT</A><DD><DT><A HREF="#lbCA">ENVIRONMENT</A><DD><DT><A HREF="#lbCB">EXIT STATUS</A><DD><DT><A HREF="#lbCC">SIGNALS</A><DD><DT><A HREF="#lbCD">JOB CONTROL</A><DD><DT><A HREF="#lbCE">PROMPTING</A><DD><DT><A HREF="#lbCF">READLINE</A><DD><DL><DT><A HREF="#lbCG">Readline Notation</A><DD><DT><A HREF="#lbCH">Readline Initialization</A><DD><DT><A HREF="#lbCI">Readline Key Bindings</A><DD><DT><A HREF="#lbCJ">Readline Variables</A><DD><DT><A HREF="#lbCK">Readline Conditional Constructs</A><DD><DT><A HREF="#lbCL">Searching</A><DD><DT><A HREF="#lbCM">Readline Command Names</A><DD><DT><A HREF="#lbCN">Commands for Moving</A><DD><DT><A HREF="#lbCO">Commands for Manipulating the History</A><DD><DT><A HREF="#lbCP">Commands for Changing Text</A><DD><DT><A HREF="#lbCQ">Killing and Yanking</A><DD><DT><A HREF="#lbCR">Numeric Arguments</A><DD><DT><A HREF="#lbCS">Completing</A><DD><DT><A HREF="#lbCT">Keyboard Macros</A><DD><DT><A HREF="#lbCU">Miscellaneous</A><DD><DT><A HREF="#lbCV">Programmable Completion</A><DD></DL><DT><A HREF="#lbCW">HISTORY</A><DD><DT><A HREF="#lbCX">HISTORY EXPANSION</A><DD><DL><DT><A HREF="#lbCY">Event Designators</A><DD><DT><A HREF="#lbCZ">Word Designators</A><DD><DT><A HREF="#lbDA">Modifiers</A><DD></DL><DT><A HREF="#lbDB">SHELL BUILTIN COMMANDS</A><DD><DT><A HREF="#lbDC">SHELL COMPATIBILITY MODE</A><DD><DT><A HREF="#lbDD">RESTRICTED SHELL</A><DD><DT><A HREF="#lbDE">SEE ALSO</A><DD><DT><A HREF="#lbDF">FILES</A><DD><DT><A HREF="#lbDG">AUTHORS</A><DD><DT><A HREF="#lbDH">BUG REPORTS</A><DD><DT><A HREF="#lbDI">BUGS</A><DD></DL><HR>This document was created by man2html from /usr/local/src/bash/bash-20220907/doc/bash.1.<BR>Time: 19 September 2022 12:02:51 EDT</BODY></HTML>