102 lines
3.8 KiB
HTML
102 lines
3.8 KiB
HTML
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
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<html>
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<head>
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<meta name="generator" content="HTML Tidy, see www.w3.org">
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<meta http-equiv="Content-Type" content=
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"text/html; charset=utf-8">
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<title>Parameters</title>
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<LINK rel="stylesheet" type="text/css" href="../rzahg/ic.css">
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</HEAD>
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<body bgcolor="#FFFFFF">
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<!-- Java sync-link -->
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<SCRIPT LANGUAGE="Javascript" SRC="../rzahg/synch.js" TYPE="text/javascript"></SCRIPT>
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<h2>Parameters</h2>
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<p>A parameter is used to store data. You can access the value of a
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parameter by preceding its name with a dollar sign
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(<strong>$</strong>) and surrounding the name with brackets
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(<strong>{ }</strong>). The brackets are optional when the name is
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a single digit, is a special parameter, or is a single identifier.
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See <a href="paramexp.htm">"Parameter expansion"</a> for more
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information about expanding the value of a parameter.</p>
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<p><strong>Positional parameters</strong></p>
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<p>A positional parameter is a decimal number starting from one.
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Initially, <strong>qsh</strong> sets the positional parameters to
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the command line arguments that follow the name of the shell
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script. The positional parameters are temporarily replaced when a
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shell function is called and can be reassigned using the <a href=
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"set.htm">set</a> and <a href="shift.htm">shift</a> utilities.</p>
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<p><strong>Special parameters</strong></p>
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<p>A special parameter is denoted by one of these special
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characters:</p>
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<dl>
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<dt><strong>* (Positional parameters)</strong></dt>
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<dd>(Asterisk) Expands to the positional parameters, starting from
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one. When the expansion occurs within a string with quotation marks, it
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expands to a single field with the value of each parameter
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separated by the first character of the <strong>IFS</strong>
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variable, or by a <space> if <strong>IFS</strong> is
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unset.<p></dd>
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<dt><strong>@ (Positional parameters)</strong></dt>
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<dd>(At sign) Expands to the positional parameters, starting from
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one. When the expansion occurs within quotation marks, each
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positional parameter expands as a separate argument. If there are
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no positional parameters, the expansion of <strong>@</strong>
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generates zero arguments, even when <strong>@</strong> is
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in quotation marks.<p></dd>
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<dt><strong># (Number of positional parameters)</strong></dt>
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<dd>(Number sign) Expands to the decimal number of positional
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parameters. It is initially set to the number of arguments when
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<strong>qsh</strong> is invoked. It can be changed by the <a href=
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"set.htm">set</a>, <a href="shift.htm">shift</a>, or <a href=
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"dot.htm">dot</a> utilities or by calling a function.<p></dd>
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<dt><strong>? (Exit status)</strong></dt>
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<dd>(Question mark) Expands to the decimal exit status of the most
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recent command. A value of zero indicates successful completion. A
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non-zero value indicates an error. A command ended by a signal
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number has an exit status of 128 plus the signal number.<p></dd>
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<dt><strong>- (Option flags)</strong></dt>
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<dd>(Minus) Expands to the current option flags (the single-letter
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option names concatenated into a string) as specified when <strong>
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qsh</strong> is invoked, by <a href="set.htm">set</a>, or
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implicitly by <strong>qsh</strong>.<p></dd>
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<dt><strong>$ (Process ID of current shell)</strong></dt>
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<dd>(Dollar sign) Expands to the decimal process ID of the current
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shell. A subshell retains the same value of <strong>$</strong> as
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the current shell even if the subshell is running in a different
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process.<p></dd>
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<dt><strong>! (Background process ID)</strong></dt>
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<dd>(Exclamation mark) Expands to the decimal process ID of the
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most recent background command run from the current shell. For a
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pipeline, the process ID is that of the last command in the
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pipeline.<p></dd>
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<dt><strong>0 (Name of shell script)</strong></dt>
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<dd>(Zero) Expands to the name of the shell or shell script.<p></dd>
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</dl>
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</body>
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</html>
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