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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><html><head><!-- Copyright 1997 The Open Group, All Rights Reserved --><title>wait</title></head><body bgcolor=white><center><font size=2>The Single UNIX ® Specification, Version 2<br>Copyright © 1997 The Open Group</font></center><hr size=2 noshade><h4><a name = "tag_001_014_2828"> </a>NAME</h4><blockquote>wait - await process completion</blockquote><h4><a name = "tag_001_014_2829"> </a>SYNOPSIS</h4><blockquote><pre><code>wait <b>[</b><i>pid</i>...<b>]</b></code></pre></blockquote><h4><a name = "tag_001_014_2830"> </a>DESCRIPTION</h4><blockquote>When an asynchronous list (see<xref href=asyncl><a href="chap2.html#tag_001_009_003">Lists</a></xref>)is started by theshell, the process IDof the last command ineach element of the asynchronous listbecomes known in the current shell execution environment; see<xref href=shexenv><a href="chap2.html#tag_001_012">Shell Execution Environment</a></xref>.<p>If the<i>wait</i>utility is invoked with no operands, it will waituntil all process IDs known to the invoking shell haveterminated and exit with a zero exit status.<p>If one or more<i>pid</i>operands are specified that represent known process IDs, the<i>wait</i>utility will wait until all of them have terminated.If one or more<i>pid</i>operands are specified that represent unknown process IDs,<i>wait</i>will treat them as if theywere known process IDs that exited with exit status 127.The exit status returned by the<i>wait</i>utility will be the exit status ofthe process requested by the last<i>pid</i>operand.<p>The known process IDs are applicable only for invocations of<i>wait</i>in the current shell execution environment.</blockquote><h4><a name = "tag_001_014_2831"> </a>OPTIONS</h4><blockquote>None.</blockquote><h4><a name = "tag_001_014_2832"> </a>OPERANDS</h4><blockquote>The following operand is supported:<dl compact><dt><i>pid</i><dd>One of the following:<ol><li>The unsigned decimal integer process ID of a command,for which the utility is to wait for the termination.<li>A job control job ID (seethe <b>XBD</b> specification, <a href="../xbd/glossary.html"><b>Glossary</b> </a> )that identifies a background process group to be waited for.The job control job ID notationis applicable only for invocations of<i>wait</i>in the current shell execution environment;see<xref href=shexenv><a href="chap2.html#tag_001_012">Shell Execution Environment</a></xref>.The exit status of<i>wait</i>is determined by the last command in the pipeline.<dl><dt><b>Note:</b><dd>The job control job ID type of<i>pid</i>is available on systems supporting both thejob control optionand the User Portability Utilities Option,which applies to all XSI-conformant systems.</dl><p></ol><p></dl></blockquote><h4><a name = "tag_001_014_2833"> </a>STDIN</h4><blockquote>Not used.</blockquote><h4><a name = "tag_001_014_2834"> </a>INPUT FILES</h4><blockquote>None.</blockquote><h4><a name = "tag_001_014_2835"> </a>ENVIRONMENT VARIABLES</h4><blockquote>The following environment variables affect the execution of<i>wait</i>:<dl compact><dt><i>LANG</i><dd>Provide a default value for the internationalisation variablesthat are unset or null.If<i>LANG</i>is unset or null, the corresponding value from theimplementation-dependent default locale will be used.If any of the internationalisation variables contains an invalid setting, theutility will behave as if none of the variables had been defined.<dt><i>LC_ALL</i><dd>If set to a non-empty string value,override the values of all the other internationalisation variables.<dt><i>LC_CTYPE</i><dd>Determine thelocale for the interpretation of sequences of bytes of text data ascharacters (for example, single- as opposed to multi-byte charactersin arguments).<dt><i>LC_MESSAGES</i><dd>Determine the locale that should be used to affectthe format and contents of diagnosticmessages written to standard error.<dt><i>NLSPATH</i><dd>Determine the location of message cataloguesfor the processing of<i>LC_MESSAGES .</i></dl></blockquote><h4><a name = "tag_001_014_2836"> </a>ASYNCHRONOUS EVENTS</h4><blockquote>Default.</blockquote><h4><a name = "tag_001_014_2837"> </a>STDOUT</h4><blockquote>Not used.</blockquote><h4><a name = "tag_001_014_2838"> </a>STDERR</h4><blockquote>Used only for diagnostic messages.</blockquote><h4><a name = "tag_001_014_2839"> </a>OUTPUT FILES</h4><blockquote>None.</blockquote><h4><a name = "tag_001_014_2840"> </a>EXTENDED DESCRIPTION</h4><blockquote>None.</blockquote><h4><a name = "tag_001_014_2841"> </a>EXIT STATUS</h4><blockquote>If one or more operands were specified, all of them haveterminated or were notknown by the invoking shell, and thestatus of the last operand specified is known, then the exit status of<i>wait</i>will be the exit status information of thecommand indicated by the last operand specified.If the process terminated abnormally due to thereceipt of a signal, the exit status will be greater than 128and will be distinct from the exit status generated by othersignals, but the exact value is unspecified.(See the<i><a href="kill.html">kill</a></i><b>-l</b>option.)Otherwise, the<i>wait</i>utility will exit with one of the following values:<dl compact><dt>0<dd>The<i>wait</i>utility was invoked with no operands and allprocess IDs known by the invoking shell have terminated.<dt>1-126<dd>The<i>wait</i>utility detected an error.<dt>127<dd>The command identified by the last<i>pid</i>operand specified is unknown.</dl></blockquote><h4><a name = "tag_001_014_2842"> </a>CONSEQUENCES OF ERRORS</h4><blockquote>Default.</blockquote><h4><a name = "tag_001_014_2843"> </a>APPLICATION USAGE</h4><blockquote>On most implementations,<i>wait</i>is a shell built-in.If it is called in a subshell or separate utility execution environment,such as one of the following:<pre><code>(wait)nohup wait ...find . -exec wait ... \;</code></pre>it will return immediately because there will be no knownprocess IDs to wait for in those environments.<p>Historical implementations of interactive shells have discardedthe exit status of terminated background processes before eachshell prompt.Therefore, the status of background processes wasusually lost unless it terminated while<i>wait</i>was waiting for it.This could be a serious problem when a job that was expected torun for a long time actually terminated quickly with a syntax orinitialisation error because the exit status returned wasusually zero if the requested process ID was not found.This specification requires the implementation to keep the status ofterminated jobs available until the status is requested, so thatscripts like:<pre><code>j1&p1=$!j2&wait $p1echo Job 1 exited with status $?wait $!echo Job 2 exited with status $?</code></pre>will work without losing status on any of the jobs.The shell is allowed to discard the status of any process that itdetermines the application cannot get the process ID from the shell.It is also required to remember only{CHILD_MAX}number of processes in this way.Since the only way to get the process ID from the shellis by using the"!"shell parameter, the shell is allowed todiscard the status of an asynchronous list if$!was not referenced before another asynchronous list was started.(This means that the shell only has to keep the status of thelast asynchronous list started if the application did notreference$!.If the implementation of the shell is smartenough to determine that a reference to$!was not savedanywhere that the application can retrieve it later, it canuse this information to trim the list of saved information.Note also that a successful call to<i>wait</i>with no operandsdiscards the exit status of all asynchronous lists.)<p>If the exit status of<i>wait</i>is greater than 128, there is no wayfor the application to know if the waited-for process exitedwith that value or was killed by a signal.Since most utilitiesexit with small values, there is seldom any ambiguity.Even in the ambiguous cases, most applications just need to know thatthe asynchronous job failed; it does not matter whether itdetected an error and failed or was killed and did not completeits job normally.</blockquote><h4><a name = "tag_001_014_2844"> </a>EXAMPLES</h4><blockquote>Although the exact value used when a process is terminated by asignal is unspecified, if it is known that a signal terminated aprocess, a script can still reliably figure out which signal using<i><a href="kill.html">kill</a></i>as shown by the following script:<pre><code>sleep 1000&pid=$!kill -kill $pidwait $pidecho $pid was terminated by a SIG$(kill -l $?) signal.</code></pre><p>If the following sequence of commands is run in lessthan 31 seconds:<pre><code>sleep 257 | sleep 31 &jobs -l %%</code></pre><p>either of the following commands will return the exit statusof the second<i><a href="sleep.html">sleep</a></i>in the pipeline:<pre><code>wait <i><pid of sleep 31></i>wait %%</code></pre></blockquote><h4><a name = "tag_001_014_2845"> </a>FUTURE DIRECTIONS</h4><blockquote>None.</blockquote><h4><a name = "tag_001_014_2846"> </a>SEE ALSO</h4><blockquote><i><a href="sh.html">sh</a></i>,the <b>XSH</b> specification description of<i><a href="../xsh/waitpid.html">waitpid()</a></i>.<br></blockquote><hr size=2 noshade><center><font size=2>UNIX ® is a registered Trademark of The Open Group.<br>Copyright © 1997 The Open Group<br> [ <a href="../index.html">Main Index</a> | <a href="../xshix.html">XSH</a> | <a href="../xcuix.html">XCU</a> | <a href="../xbdix.html">XBD</a> | <a href="../cursesix.html">XCURSES</a> | <a href="../xnsix.html">XNS</a> ]</font></center><hr size=2 noshade></body></html>⌨️ 快捷键说明
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