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<title>execline: the shift program</title>
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<p>
<a href="index.html">execline</a><br />
<a href="http://skarnet.org/software/">Software</a><br />
<a href="http://skarnet.org/">www.skarnet.org</a>
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<h1> The <tt>shift</tt> program </h1>
<p>
<tt>shift</tt> shifts the positional parameters of an execline script.
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<h2> Interface </h2>
<pre>
shift [ -n <em>argn</em> ] [ -b <em>blockn</em> ] <em>prog...</em>
</pre>
<ul>
<li> <tt>shift</tt> shifts <em>argn</em> positional parameters,
then <em>blockn</em> blocks. It then execs <em>prog...</em>. </li>
<li> By default, <em>argn</em> and <em>blockn</em> are both zero;
but if neither the <tt>-n</tt> nor the <tt>-b</tt> option is given,
then <em>argn</em> is 1 and <em>blockn</em> is 0. </li>
</ul>
<h2> Details </h2>
<ul>
<li> <tt>shift</tt> reads the number of "positional parameters" in the
<tt>#</tt> environment variable. Let <em>n</em> be that number. </li>
<li> If the <tt>#</tt> environment variable is not set or does not
contain a valid number, or one of the <tt>0</tt>, <tt>1</tt>, ...,
<tt><em>n</em></tt> environment variables is not set, <tt>shift</tt>
exits 100 with an error message. </li>
<li> <tt>shift</tt> calculates a shift value <em>m</em>, corresponding
to <em>argn</em> arguments followed by enough arguments to make
<em>blockn</em> blocks. </li>
<li> It shifts the positional parameters <em>m</em> times: the
value of the <tt><em>m</em>+1</tt> variable becomes the value of the
<tt>1</tt> variable, <tt><em>m</em>+2</tt> becomes <tt>2</tt> and so on,
and <tt>#</tt> is set to <em>n</em>-<em>m</em> (floored at zero). </li>
<li> <tt>shift</tt> then execs into <em>prog...</em>. </li>
</ul>
<h2> Notes </h2>
<ul>
<li> <tt>shift</tt> is a standard shell builtin. Be careful if you
want to use it outside of an execline script. </li>
<li> The <tt>-b</tt> option is only useful to implement execline
commands in the execline language. You shouldn't normally have to
use it. </li>
</ul>
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