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<title>execline: the loopwhilex command</title>
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<p>
<a href="index.html">execline</a><br />
<a href="//skarnet.org/software/">Software</a><br />
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<h1> The <tt>loopwhilex</tt> program </h1>
<p>
<tt>loopwhilex</tt> performs a conditional loop.
</p>
<h2> Interface </h2>
<pre>
loopwhilex [ -n ] [ -o <em>okcodes</em> | -x <em>breakcodes</em> ] <em>prog...</em>
</pre>
<ul>
<li> <tt>loopwhilex</tt> runs <em>prog...</em> as a child process and
waits for it to complete. </li>
<li> As long as <em>prog</em> exits zero, <tt>loopwhile</tt> runs it again. </li>
<li> <tt>loopwhilex</tt> then exits with an
<a href="exitcodes.html">approximation</a> of the last <em>prog</em>
invocation's exit code. </li>
</ul>
<h2> Options </h2>
<ul>
<li> <tt>-o</tt> <em>okcodes</em> : <em>okcodes</em> must
be a comma-separated list of exit codes. <tt>loopwhilex</tt> will keep
looping as long as <em>prog</em> exits with one of the codes in
<em>okcodes</em>. </li>
<li> <tt>-x</tt> <em>breakcodes</em> : like the previous
option, but with inverted meaning - the listed exit codes are codes
that will break the loop and exit, and the unlisted exit codes will keep
the loop running. </li>
<li> <tt>-n</tt> : negate the test. This option is now redundant,
and may disappear soon. </li>
</ul>
<h2> Notes </h2>
<ul>
<li> <tt>loopwhilex <em>prog</em>...</tt> is equivalent to <tt>loopwhilex -n -x 0 <em>prog...</em></tt>
and <tt>loopwhilex -o 0 <em>prog</em>...</tt> </li>
<li> Be careful: execline <strong>maintains no state</strong>, in particular it
uses <strong>no real variables</strong>, and environment will
be of no use here since every instance of <em>prog...</em> runs as a separate
child process. To avoid being stuck in an infinite loop, <em>prog...</em>
should modify some external state - for instance, the filesystem. </li>
</ul>
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