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  <title>execline: the loopwhilex command</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/">skarnet.org</a>
</p>

<h1> The <tt>loopwhilex</tt> program </h1>

<p>
<tt>loopwhilex</tt> performs a conditional loop.
</p>

<h2> Interface </h2>

<pre>
     loopwhilex [ -n ] [ -x <em>exitcodes</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 0. If <em>prog</em> was killed by a signal,
<tt>loopwhilex</tt> exits that signal's number instead. </li>
</ul>

<h2> Options </h2>

<ul>
 <li> <tt>-x</tt>&nbsp;<em>exitcodes</em>&nbsp;: <em>exitcodes</em> must be a comma-separated
list of valid exit codes. If this option is given, <tt>loopwhilex</tt> will run as long as
<em>prog...</em>'s exit code is <em>not</em> listed in <em>breakcodes</em>. </li>
 <li> <tt>-n</tt>&nbsp;: negate the test: run <em>prog...</em> as long as it exits non-zero
(or exits a code that <em>is</em> listed in <em>breakcodes</em>). </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>. </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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