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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><meta name="generator" content="HTML Tidy, see www.w3.org"><meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 --><!-- Copyright (c) 2001-2004 IEEE and The Open Group, All Rights Reserved --><title>time</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="time"></a> <a name="tag_04_141"></a><!-- time --> <!--header start--><center><font size="2">The Open Group Base Specifications Issue 6<br>IEEE Std 1003.1, 2004 Edition<br>Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.</font></center><!--header end--><hr size="2" noshade><h4><a name="tag_04_141_01"></a>NAME</h4><blockquote>time - time a simple command</blockquote><h4><a name="tag_04_141_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><div class="box"><code><tt><sup>[<a href="javascript:open_code('UP')">UP</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> time</tt> <b>[</b><tt>-p</tt><b>]</b> <i>utility</i><b>[</b><i>argument</i><tt>...</tt><b>]</b><tt><img src="../images/opt-end.gif" alt="[Option End]" border="0"></tt></code></div></blockquote><h4><a name="tag_04_141_03"></a>DESCRIPTION</h4><blockquote><p>The <i>time</i> utility shall invoke the utility named by the <i>utility</i> operand with arguments supplied as the<i>argument</i> operands and write a message to standard error that lists timing statistics for the utility. The message shallinclude the following information:</p><ul><li><p>The elapsed (real) time between invocation of <i>utility</i> and its termination.</p></li><li><p>The User CPU time, equivalent to the sum of the <i>tms_utime</i> and <i>tms_cutime</i> fields returned by the <a href="../functions/times.html"><i>times</i>()</a> function defined in the System Interfaces volume of IEEE Std 1003.1-2001 forthe process in which <i>utility</i> is executed.</p></li><li><p>The System CPU time, equivalent to the sum of the <i>tms_stime</i> and <i>tms_cstime</i> fields returned by the <a href="../functions/times.html"><i>times</i>()</a> function for the process in which <i>utility</i> is executed.</p></li></ul><p>The precision of the timing shall be no less than the granularity defined for the size of the clock tick unit on the system, butthe results shall be reported in terms of standard time units (for example, 0.02 seconds, 00:00:00.02, 1m33.75s, 365.21 seconds),not numbers of clock ticks.</p><p>When <i>time</i> is used as part of a pipeline, the times reported are unspecified, except when it is the sole command within agrouping command (see <a href="xcu_chap02.html#tag_02_09_04_01"><i>Grouping Commands</i></a>) in that pipeline. For example, thecommands on the left are unspecified; those on the right report on utilities <b>a</b> and <b>c</b>, respectively:</p><pre><tt>time a | b | c { time a } | b | ca | b | time c a | b | (time c)</tt></pre></blockquote><h4><a name="tag_04_141_04"></a>OPTIONS</h4><blockquote><p>The <i>time</i> utility shall conform to the Base Definitions volume of IEEE Std 1003.1-2001, <a href="../basedefs/xbd_chap12.html#tag_12_02">Section 12.2, Utility Syntax Guidelines</a>.</p><p>The following option shall be supported:</p><dl compact><dt><b>-p</b></dt><dd>Write the timing output to standard error in the format shown in the STDERR section.</dd></dl></blockquote><h4><a name="tag_04_141_05"></a>OPERANDS</h4><blockquote><p>The following operands shall be supported:</p><dl compact><dt><i>utility</i></dt><dd>The name of a utility that is to be invoked. If the <i>utility</i> operand names any of the special built-in utilities in <ahref="xcu_chap02.html#tag_02_14"><i>Special Built-In Utilities</i></a> , the results are undefined.</dd><dt><i>argument</i></dt><dd>Any string to be supplied as an argument when invoking the utility named by the <i>utility</i> operand.</dd></dl></blockquote><h4><a name="tag_04_141_06"></a>STDIN</h4><blockquote><p>Not used.</p></blockquote><h4><a name="tag_04_141_07"></a>INPUT FILES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_141_08"></a>ENVIRONMENT VARIABLES</h4><blockquote><p>The following environment variables shall affect the execution of <i>time</i>:</p><dl compact><dt><i>LANG</i></dt><dd>Provide a default value for the internationalization variables that are unset or null. (See the Base Definitions volume ofIEEE Std 1003.1-2001, <a href="../basedefs/xbd_chap08.html#tag_08_02">Section 8.2, Internationalization Variables</a> forthe precedence of internationalization variables used to determine the values of locale categories.)</dd><dt><i>LC_ALL</i></dt><dd>If set to a non-empty string value, override the values of all the other internationalization variables.</dd><dt><i>LC_CTYPE</i></dt><dd>Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte asopposed to multi-byte characters in arguments).</dd><dt><i>LC_MESSAGES</i></dt><dd>Determine the locale that should be used to affect the format and contents of diagnostic and informative messages written tostandard error.</dd><dt><i>LC_NUMERIC</i></dt><dd>Determine the locale for numeric formatting.</dd><dt><i>NLSPATH</i></dt><dd><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">Determine the location of message catalogs for the processing of <i>LC_MESSAGES .</i> <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd><dt><i>PATH</i></dt><dd>Determine the search path that shall be used to locate the utility to be invoked; see the Base Definitions volume ofIEEE Std 1003.1-2001, <a href="../basedefs/xbd_chap08.html">Chapter 8, Environment Variables</a>.</dd></dl></blockquote><h4><a name="tag_04_141_09"></a>ASYNCHRONOUS EVENTS</h4><blockquote><p>Default.</p></blockquote><h4><a name="tag_04_141_10"></a>STDOUT</h4><blockquote><p>Not used.</p></blockquote><h4><a name="tag_04_141_11"></a>STDERR</h4><blockquote><p>The standard error shall be used to write the timing statistics. If <b>-p</b> is specified, the following format shall be usedin the POSIX locale:</p><pre><tt>"real %f\nuser %f\nsys %f\n", <</tt><i>real seconds</i><tt>>, <</tt><i>user seconds</i><tt>>, <</tt><i>system seconds</i><tt>></tt></pre><p>where each floating-point number shall be expressed in seconds. The precision used may be less than the default six digits of<tt>%f</tt>, but shall be sufficiently precise to accommodate the size of the clock tick on the system (for example, if there were60 clock ticks per second, at least two digits shall follow the radix character). The number of digits following the radixcharacter shall be no less than one, even if this always results in a trailing zero. The implementation may append white space andadditional information following the format shown here.</p></blockquote><h4><a name="tag_04_141_12"></a>OUTPUT FILES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_141_13"></a>EXTENDED DESCRIPTION</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_141_14"></a>EXIT STATUS</h4><blockquote><p>If the <i>utility</i> utility is invoked, the exit status of <i>time</i> shall be the exit status of <i>utility</i>; otherwise,the <i>time</i> utility shall exit with one of the following values:</p><dl compact><dt>1-125</dt><dd>An error occurred in the <i>time</i> utility.</dd><dt> 126</dt><dd>The utility specified by <i>utility</i> was found but could not be invoked.</dd><dt> 127</dt><dd>The utility specified by <i>utility</i> could not be found.</dd></dl></blockquote><h4><a name="tag_04_141_15"></a>CONSEQUENCES OF ERRORS</h4><blockquote><p>Default.</p></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_04_141_16"></a>APPLICATION USAGE</h4><blockquote><p>The <a href="../utilities/command.html"><i>command</i></a>, <a href="../utilities/env.html"><i>env</i></a>, <a href="../utilities/nice.html"><i>nice</i></a>, <a href="../utilities/nohup.html"><i>nohup</i></a>, <i>time</i>, and <a href="../utilities/xargs.html"><i>xargs</i></a> utilities have been specified to use exit code 127 if an error occurs so thatapplications can distinguish "failure to find a utility" from "invoked utility exited with an error indication". The value 127was chosen because it is not commonly used for other meanings; most utilities use small values for "normal error conditions" andthe values above 128 can be confused with termination due to receipt of a signal. The value 126 was chosen in a similar manner toindicate that the utility could be found, but not invoked. Some scripts produce meaningful error messages differentiating the 126and 127 cases. The distinction between exit codes 126 and 127 is based on KornShell practice that uses 127 when all attempts to<i>exec</i> the utility fail with [ENOENT], and uses 126 when any attempt to <i>exec</i> the utility fails for any otherreason.</p></blockquote><h4><a name="tag_04_141_17"></a>EXAMPLES</h4><blockquote><p>It is frequently desirable to apply <i>time</i> to pipelines or lists of commands. This can be done by placing pipelines andcommand lists in a single file; this file can then be invoked as a utility, and the <i>time</i> applies to everything in thefile.</p><p>Alternatively, the following command can be used to apply <i>time</i> to a complex command:</p><pre><tt>time sh -c '</tt><i>complex-command-line</i><tt>'</tt></pre></blockquote><h4><a name="tag_04_141_18"></a>RATIONALE</h4><blockquote><p>When the <i>time</i> utility was originally proposed to be included in the ISO POSIX-2:1993 standard, questions were raisedabout its suitability for inclusion on the grounds that it was not useful for conforming applications, specifically:</p><ul><li><p>The underlying CPU definitions from the System Interfaces volume of IEEE Std 1003.1-2001 are vague, so the numericoutput could not be compared accurately between systems or even between invocations.</p></li><li><p>The creation of portable benchmark programs was outside the scope this volume of IEEE Std 1003.1-2001.</p></li></ul><p>However, <i>time</i> does fit in the scope of user portability. Human judgement can be applied to the analysis of the output,and it could be very useful in hands-on debugging of applications or in providing subjective measures of system performance. Henceit has been included in this volume of IEEE Std 1003.1-2001.</p><p>The default output format has been left unspecified because historical implementations differ greatly in their style ofdepicting this numeric output. The <b>-p</b> option was invented to provide scripts with a common means of obtaining thisinformation.</p><p>In the KornShell, <i>time</i> is a shell reserved word that can be used to time an entire pipeline, rather than just a simplecommand. The POSIX definition has been worded to allow this implementation. Consideration was given to invalidating this approachbecause of the historical model from the C shell and System V shell. However, since the System V <i>time</i> utility historicallyhas not produced accurate results in pipeline timing (because the constituent processes are not all owned by the same parentprocess, as allowed by POSIX), it did not seem worthwhile to break historical KornShell usage.</p><p>The term <i>utility</i> is used, rather than <i>command</i>, to highlight the fact that shell compound commands, pipelines,special built-ins, and so on, cannot be used directly. However, <i>utility</i> includes user application programs and shellscripts, not just the standard utilities.</p></blockquote><h4><a name="tag_04_141_19"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_141_20"></a>SEE ALSO</h4><blockquote><p><a href="xcu_chap02.html#tag_02"><i>Shell Command Language</i></a>, <a href="sh.html"><i>sh</i></a>, the System Interfacesvolume of IEEE Std 1003.1-2001, <a href="../functions/times.html"><i>times</i>()</a></p></blockquote><h4><a name="tag_04_141_21"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 2.</p></blockquote><h4><a name="tag_04_141_22"></a>Issue 6</h4><blockquote><p>This utility is marked as part of the User Portability Utilities option.</p></blockquote><div class="box"><em>End of informative text.</em></div><hr size="2" noshade><center><font size="2"><!--footer start-->UNIX ® is a registered Trademark of The Open Group.<br>POSIX ® is a registered Trademark of The IEEE.<br>[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href="../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>]</font></center><!--footer end--><hr size="2" noshade></body></html>⌨️ 快捷键说明
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