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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) 2001-2003 The Open Group, All Rights Reserved --><title>touch</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="touch"></a> <a name="tag_04_143"></a><!-- touch --> <!--header start--><center><font size="2">The Open Group Base Specifications Issue 6<br>IEEE Std 1003.1, 2003 Edition<br>Copyright © 2001-2003 The IEEE and The Open Group, All Rights reserved.</font></center><!--header end--><hr size="2" noshade><h4><a name="tag_04_143_01"></a>NAME</h4><blockquote>touch - change file access and modification times</blockquote><h4><a name="tag_04_143_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><p><code><tt>touch</tt> <b>[</b><tt>-acm</tt><b>][</b> <tt>-r</tt> <i>ref_file</i><tt>| -t</tt> <i>time</i><b>]</b><i>file</i><tt>...</tt></code></p></blockquote><h4><a name="tag_04_143_03"></a>DESCRIPTION</h4><blockquote><p>The <i>touch</i> utility shall change the modification times, access times, or both of files. The modification time shall beequivalent to the value of the <i>st_mtime</i> member of the <b>stat</b> structure for a file, as described in the SystemInterfaces volume of IEEE Std 1003.1-2001; the access time shall be equivalent to the value of <i>st_atime</i>.</p><p>The time used can be specified by the <b>-t</b> <i>time</i> option-argument, the corresponding time fields of the filereferenced by the <b>-r</b> <i>ref_file</i> option-argument, or the <i>date_time</i> operand, as specified in the followingsections. If none of these are specified, <i>touch</i> shall use the current time (the value returned by the equivalent of the <ahref="../functions/time.html"><i>time</i>()</a> function defined in the System Interfaces volume ofIEEE Std 1003.1-2001).</p><p>For each <i>file</i> operand, <i>touch</i> shall perform actions equivalent to the following functions defined in the SystemInterfaces volume of IEEE Std 1003.1-2001:</p><ol><li><p>If <i>file</i> does not exist, a <a href="../functions/creat.html"><i>creat</i>()</a> function call is made with the <i>file</i>operand used as the <i>path</i> argument and the value of the bitwise-inclusive OR of S_IRUSR, S_IWUSR, S_IRGRP, S_IWGRP, S_IROTH,and S_IWOTH used as the <i>mode</i> argument.</p></li><li><p>The <a href="../functions/utime.html"><i>utime</i>()</a> function is called with the following arguments:</p><ol type="a"><li><p>The <i>file</i> operand is used as the <i>path</i> argument.</p></li><li><p>The <b>utimbuf</b> structure members <i>actime</i> and <i>modtime</i> are determined as described in the OPTIONS section.</p></li></ol></li></ol></blockquote><h4><a name="tag_04_143_04"></a>OPTIONS</h4><blockquote><p>The <i>touch</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 options shall be supported:</p><dl compact><dt><b>-a</b></dt><dd>Change the access time of <i>file</i>. Do not change the modification time unless <b>-m</b> is also specified.</dd><dt><b>-c</b></dt><dd>Do not create a specified <i>file</i> if it does not exist. Do not write any diagnostic messages concerning thiscondition.</dd><dt><b>-m</b></dt><dd>Change the modification time of <i>file</i>. Do not change the access time unless <b>-a</b> is also specified.</dd><dt><b>-r </b> <i>ref_file</i></dt><dd>Use the corresponding time of the file named by the pathname <i>ref_file</i> instead of the current time.</dd><dt><b>-t </b> <i>time</i></dt><dd>Use the specified <i>time</i> instead of the current time. The option-argument shall be a decimal number of the form: <pre><b>[[</b><i>CC</i><b>]</b><i>YY</i><b>]</b><i>MMDDhhmm</i><b>[</b><tt>.</tt><i>SS</i><b>]</b></pre><p>where each two digits represents the following:</p><dl compact><dt><i>MM</i></dt><dd>The month of the year [01,12].</dd><dt><i>DD</i></dt><dd>The day of the month [01,31].</dd><dt><i>hh</i></dt><dd>The hour of the day [00,23].</dd><dt><i>mm</i></dt><dd>The minute of the hour [00,59].</dd><dt><i>CC</i></dt><dd>The first two digits of the year (the century).</dd><dt><i>YY</i></dt><dd>The second two digits of the year.</dd><dt><i>SS</i></dt><dd>The second of the minute [00,60].</dd></dl><p>Both <i>CC</i> and <i>YY</i> shall be optional. If neither is given, the current year shall be assumed. If <i>YY</i> isspecified, but <i>CC</i> is not, <i>CC</i> shall be derived as follows:</p><center><table border="1" cellpadding="3" align="center"><tr valign="top"><th align="center"><p class="tent"><b>If <i>YY</i> is:</b></p></th><th align="center"><p class="tent"><b><i>CC</i> becomes:</b></p></th></tr><tr valign="top"><td align="center"><p class="tent">[69,99]</p></td><td align="left"><p class="tent">19</p></td></tr><tr valign="top"><td align="center"><p class="tent">[00,68]</p></td><td align="left"><p class="tent">20</p></td></tr></table></center><basefont size="2"> <dl><dt><b>Note:</b></dt><dd>It is expected that in a future version of IEEE Std 1003.1-2001 the default century inferred from a 2-digit year willchange. (This would apply to all commands accepting a 2-digit year as input.)</dd></dl><basefont size="3"> <p>The resulting time shall be affected by the value of the <i>TZ</i> environment variable. If the resulting time value precedesthe Epoch, <i>touch</i> shall exit immediately with an error status. The range of valid times past the Epoch isimplementation-defined, but it shall extend to at least the time 0 hours, 0 minutes, 0 seconds, January 1, 2038, CoordinatedUniversal Time. Some implementations may not be able to represent dates beyond January 18, 2038, because they use <b>signed int</b>as a time holder.</p><p>The range for <i>SS</i> is [00,60] rather than [00,59] because of leap seconds. If <i>SS</i> is 60, and the resulting time, asaffected by the <i>TZ</i> environment variable, does not refer to a leap second, the resulting time shall be one second after atime where <i>SS</i> is 59. If <i>SS</i> is not given a value, it is assumed to be zero.</p></dd></dl><p>If neither the <b>-a</b> nor <b>-m</b> options were specified, <i>touch</i> shall behave as if both the <b>-a</b> and <b>-m</b>options were specified.</p></blockquote><h4><a name="tag_04_143_05"></a>OPERANDS</h4><blockquote><p>The following operands shall be supported:</p><dl compact><dt><i>file</i></dt><dd>A pathname of a file whose times shall be modified.</dd></dl></blockquote><h4><a name="tag_04_143_06"></a>STDIN</h4><blockquote><p>Not used.</p></blockquote><h4><a name="tag_04_143_07"></a>INPUT FILES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_143_08"></a>ENVIRONMENT VARIABLES</h4><blockquote><p>The following environment variables shall affect the execution of <i>touch</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 messages written to standarderror.</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>TZ</i></dt><dd>Determine the timezone to be used for interpreting the <i>time</i> option-argument. If <i>TZ</i> is unset or null, anunspecified default timezone shall be used.</dd></dl></blockquote><h4><a name="tag_04_143_09"></a>ASYNCHRONOUS EVENTS</h4><blockquote><p>Default.</p></blockquote><h4><a name="tag_04_143_10"></a>STDOUT</h4><blockquote><p>Not used.</p></blockquote><h4><a name="tag_04_143_11"></a>STDERR</h4><blockquote><p>The standard error shall be used only for diagnostic messages.</p></blockquote><h4><a name="tag_04_143_12"></a>OUTPUT FILES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_143_13"></a>EXTENDED DESCRIPTION</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_143_14"></a>EXIT STATUS</h4><blockquote><p>The following exit values shall be returned:</p><dl compact><dt> 0</dt><dd>The utility executed successfully and all requested changes were made.</dd><dt>>0</dt><dd>An error occurred.</dd></dl></blockquote><h4><a name="tag_04_143_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_143_16"></a>APPLICATION USAGE</h4><blockquote><p>The interpretation of time is taken to be <i>seconds since the Epoch</i> (see the Base Definitions volume ofIEEE Std 1003.1-2001, <a href="../basedefs/xbd_chap04.html#tag_04_14">Section 4.14, Seconds Since the Epoch</a>). Itshould be noted that implementations conforming to the System Interfaces volume of IEEE Std 1003.1-2001 do not take leapseconds into account when computing seconds since the Epoch. When <i>SS</i>=60 is used, the resulting time always refers to 1 plus<i>seconds since the Epoch</i> for a time when <i>SS</i>=59.</p><p>Although the <b>-t</b> <i>time</i> option-argument specifies values in 1969, the access time and modification time fields aredefined in terms of seconds since the Epoch (00:00:00 on 1 January 1970 UTC). Therefore, depending on the value of <i>TZ</i> when<i>touch</i> is run, there is never more than a few valid hours in 1969 and there need not be any valid times in 1969.</p><p>One ambiguous situation occurs if <b>-t</b> <i>time</i> is not specified, <b>-r</b> <i>ref_file</i> is not specified, and thefirst operand is an eight or ten-digit decimal number. A portable script can avoid this problem by using:</p><pre><tt>touch -- file</tt></pre><p>or:</p><pre><tt>touch ./file</tt></pre><p>in this case.</p></blockquote><h4><a name="tag_04_143_17"></a>EXAMPLES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_143_18"></a>RATIONALE</h4><blockquote><p>The functionality of <i>touch</i> is described almost entirely through references to functions in the System Interfaces volumeof IEEE Std 1003.1-2001. In this way, there is no duplication of effort required for describing such side effects as therelationship of user IDs to the user database, permissions, and so on.</p><p>There are some significant differences between the <i>touch</i> utility in this volume of IEEE Std 1003.1-2001 andthose in System V and BSD systems. They are upwards-compatible for historical applications from both implementations:</p><ol><li><p>In System V, an ambiguity exists when a pathname that is a decimal number leads the operands; it is treated as a time value. InBSD, no <i>time</i> value is allowed; files may only be <i>touch</i>ed to the current time. The <b>-t</b> <i>time</i> constructsolves these problems for future conforming applications (note that the <b>-t</b> option is not historical practice).</p></li><li><p>The inclusion of the century digits, <i>CC</i>, is also new. Note that a ten-digit <i>time</i> value is treated as if <i>YY</i>,and not <i>CC</i>, were specified. The caveat about the range of dates following the Epoch was included as recognition that someimplementations are not able to represent dates beyond 18 January 2038 because they use <b>signed int</b> as a time holder.</p></li></ol><p>The <b>-r</b> option was added because several comments requested this capability. This option was named <b>-f</b> in an earlyproposal, but was changed because the <b>-f</b> option is used in the BSD version of <i>touch</i> with a different meaning.</p><p>At least one historical implementation of <i>touch</i> incremented the exit code if <b>-c</b> was specified and the file did notexist. This volume of IEEE Std 1003.1-2001 requires exit status zero if no errors occur.</p></blockquote><h4><a name="tag_04_143_19"></a>FUTURE DIRECTIONS</h4><blockquote><p>Applications should use the <b>-r</b> or <b>-t</b> options.</p></blockquote><h4><a name="tag_04_143_20"></a>SEE ALSO</h4><blockquote><p><a href="date.html"><i>date</i></a> , the System Interfaces volume of IEEE Std 1003.1-2001, <a href="../functions/creat.html"><i>creat</i>()</a>, <a href="../functions/time.html"><i>time</i>()</a>, <a href="../functions/utime.html"><i>utime</i>()</a>, the Base Definitions volume of IEEE Std 1003.1-2001, <a href="../basedefs/sys/stat.h.html"><i><sys/stat.h></i></a></p></blockquote><h4><a name="tag_04_143_21"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 2.</p></blockquote><h4><a name="tag_04_143_22"></a>Issue 6</h4><blockquote><p>The obsolescent <i>date_time</i> operand is removed.</p><p>The Open Group Corrigendum U027/1 is applied. This extends the range of valid time past the Epoch to at least the time 0 hours,0 minutes, 0 seconds, January 1, 2038, Coordinated Universal Time. This is a new requirement on POSIX implementations.</p><p>The range for seconds is changed from [00,61] to [00,60] to align with the ISO/IEC 9899:1999 standard, and to allow forpositive leap seconds.</p></blockquote><div class="box"><em>End of informative text.</em></div><hr><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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