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<h1> The <tt>wait</tt> program </h1>
<p>
<tt>wait</tt> waits for a set of children, then executes a program.
</p>
<h2> Interface </h2>
<p>
In an <a href="execlineb.html">execlineb</a> script:
</p>
<pre>
wait [ -I | -i ] [ -a | -o ] [ -r | -t <em>timeout</em> ] { [ <em>pids...</em> ] } <em>prog...</em>
</pre>
<ul>
<li> <tt>wait</tt> reads a list of <em>pids</em> in a
(possibly empty) <a href="el_semicolon.html">block</a>,
and unquotes it. </li>
<li> <tt>wait</tt> waits for every child whose pid is
listed in <em>pids...</em>. If <em>pids...</em> is an
empty list, it waits for every child process it has. </li>
<li><tt>wait</tt> then execs into <em>prog...</em>. </li>
</ul>
<h2> Options </h2>
<ul>
<li> <tt>-r</tt> : equivalent to <tt>-t 0</tt>. Do not
pause: only reap processes that are already dead when <tt>wait</tt>
is invoked. </li>
<li> <tt>-t</tt> <em>timeout</em> : wait for a maximum
of <em>timeout</em> milliseconds. If there still are living processes
among <em>pids...</em> (or among <tt>wait</tt>'s children if
<em>pids...</em> is an empty list), after <em>timeout</em>
milliseconds, they will not be reaped. </li>
<li> <tt>-I</tt> : loose. If <tt>wait</tt> times out while
waiting for children to die, it will still
exec into <em>prog...</em>. This is the default. </li>
<li> <tt>-i</tt> : strict. If <tt>wait</tt> times out, it
will print an error message and exit 99. </li>
<li> <tt>-o</tt> : wait for <em>one</em> of the listed
<em>pids</em> — exec into <em>prog</em> as soon as one of the
listed children dies. (If no pid is listed, wait for one child to die.)
The <tt>!</tt> environment variable will be set to the
pid that died, and the <tt>?</tt> environment variable will contain an
<a href="exitcodes.html">approximation</a> of its exit code. If no
listed child has died before <tt>wait</tt> has to exec (either because
it timed out or it has no suitable children left), the <tt>?</tt> and
<tt>!</tt> environment variables are unset. </li>
<li> <tt>-a</tt> : wait for <em>all</em> of the listed <em>pids</em>.
Do not touch the <tt>!</tt> or <tt>?</tt> variables. This is the default. </li>
</ul>
<h2> Notes </h2>
<ul>
<li> For <a href="https://pubs.opengroup.org/onlinepubs/9699919799/utilities/wait.html">POSIX
compatibility</a>, <tt>wait</tt> also works when it cannot find a block.
In that case, all the options are still supported and have the same
effect, but the rest of the command line is interpreted as <em>pids...</em>
arguments and <tt>wait</tt> does not execute into a program; instead, it exits
with a conforming exit code. </li>
</ul>
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