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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>touch</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_2296"> </a>NAME</h4><blockquote>touch - change file access and modification times</blockquote><h4><a name = "tag_001_014_2297"> </a>SYNOPSIS</h4><blockquote><pre><code>touch <b>[</b>-acm<b>][</b> -r <i>ref_file</i>| -t <i>time</i><b>]</b><i> file</i>...touch <b>[</b>-acm<b>][</b><i>date_time</i><b>]</b><i> file</i>...</code></pre></blockquote><h4><a name = "tag_001_014_2298"> </a>DESCRIPTION</h4><blockquote>The<i>touch</i>utility will change the modification times, access timesor both of files.The modification time is equivalent to the value of the<i>st_mtime</i>member of the<i>stat</i>structure for a file, as described in the <b>XSH</b> specification;the access time is equivalent to the value of<i>st_atime</i>.<p>The time used can be specified by the<b>-t</b> <i>time</i>option-argument, thecorresponding time fields of the file referenced by the<b>-r</b> <i>ref_file</i>option-argument, or the<i>date_time</i>operand, as specified inthe following sections.If none of these are specified,<i>touch</i>will usethe current time (the value returned by the equivalent of the <b>XSH</b> specification<i><a href="../xsh/time.html">time()</a></i>function).<p>For each<i>file</i>operand,<i>touch</i>will perform actions equivalent to the following functions defined in the <b>XSH</b> specification:<ol><p><li>If<i>file</i>does not exist, a<i><a href="../xsh/creat.html">creat()</a></i>function call is made with the<i>file</i>operand used as the<i>path</i>argument and the value of the bitwise inclusiveOR of S_IRUSR, S_IWUSR, S_IRGRP, S_IWGRP, S_IROTH andS_IWOTH used as the<i>mode</i>argument.<p><li>The<i><a href="../xsh/utime.html">utime()</a></i>function is called with the following arguments:<ol type = a><p><li>The<i>file</i>operand is used as the<i>path</i>argument.<p><li>The<i>utimbuf</i>structure members<i>actime</i>and<i>modtime</i>are determined as described in the OPTIONS section.<p></ol><p></ol></blockquote><h4><a name = "tag_001_014_2299"> </a>OPTIONS</h4><blockquote>The<i>touch</i>utility supports the <b>XBD</b> specification, <a href="../xbd/utilconv.html#usg"><b>Utility Syntax Guidelines</b> </a> .<p>The following options are supported:<dl compact><dt><b>-a</b><dd>Change the access time of<i>file</i>.Do not change the modification time unless<b>-m</b>is also specified.<dt><b>-c</b><dd>Do not create a specified<i>file</i>if it does not exist.Do not write any diagnostic messagesconcerning this condition.<dt><b>-m</b><dd>Change the modification time of<i>file</i>.Do not change the access time unless<b>-a</b>is also specified.<dt><b>-r </b><i>ref_file</i><dd>Use the corresponding time ofthe file named by the pathname<i>ref_file</i>instead of the current time.<dt><b>-t </b><i>time</i><dd>Use the specified<i>time</i>instead of the current time.The option-argument will be a decimal number of the form:<pre><code><b>[[</b><i>CC</i><b>]</b><i>YY</i><b>]</b><i>MMDDhhmm</i><b>[</b>.<i>SS</i><b>]</b></code></pre>where each two digits represents the following:<dl compact><dt><i>MM</i><dd>The month of the year[01-12].<dt><i>DD</i><dd>The day of the month[01-31].<dt><i>hh</i><dd>The hour of the day[00-23].<dt><i>mm</i><dd>The minute of the hour[00-59].<dt><i>CC</i><dd>The first two digits of the year (the century).<dt><i>YY</i><dd>The second two digits of the year.<dt><i>SS</i><dd>The second of the minute [00-61].</dl><p>Both<i>CC</i>and<i>YY</i>are optional.If neither is given, the current year will be assumed.If<i>YY</i>is specified, but<i>CC</i>is not,<i>CC</i>will be derived as follows:<pre><table bordercolor=#000000 border=1 align=center><tr valign=top><th align=center><b>If YY is:</b><th align=center><b>CC becomes:</b><tr valign=top><td align=center>69-99<td align=center>19<tr valign=top><td align=center>00-68<td align=center>20</table></pre><p>The resulting time will be affected by the value of the<i>TZ</i>environment variable.If the resulting time value precedes the Epoch,<i>touch</i>will exit immediately with an error status.The range of valid times past the Epoch is implementation-dependent,but will extend to at leastthe time 0 hours, 0 minutes, 0 seconds, January 1, 2038,Coordinated Universal Time.Some systems will not be able to represent dates beyond theJanuary 18, 2038,because they use<b>signed int</b>as a time holder.<p>The range for<i>SS</i>is (00-61) rather than (00-59) because of leap seconds.If<i>SS</i>is 60 or 61, and the resulting time, as affected by the<i>TZ</i>environment variable, does not refer to a leap second,the resulting time will beone or two seconds after a time where<i>SS</i>is 59.If<i>SS</i>is not given a value, it is assumed to be zero.<p></dl><p>If neither the<b>-a</b>nor<b>-m</b>options were specified,<i>touch</i>will behave as if both the<b>-a</b>and<b>-m</b>options were specified.</blockquote><h4><a name = "tag_001_014_2300"> </a>OPERANDS</h4><blockquote>The following operands are supported:<dl compact><dt><i>file</i><dd>A pathname of a file whose times are to be modified.<dt><i>date_time</i><dd>Use the specified<i>date_time</i>instead of the current time.The operand is a decimal number of the form:<pre><code><i>MMDDhhmm</i><b>[</b><i>yy</i><b>]</b></code></pre>where<i>MM</i>,<i>DD</i>,<i>hh</i>,and<i>mm</i>are as described for the<i>time</i>option-argument to the<b>-t</b>option and the optional<i>yy</i>is interpreted as follows:<dl compact><dt> <dd>If not specified, the current year will be used.If<i>yy</i>is in the range 69-99, the year 1969-1999,respectively, will be used.Otherwise, the results are unspecified.</dl><p>If no<b>-r</b>option is specified, no<b>-t</b>option is specified, at least two operandsare specified, and the first operand is an eight- or ten-digit decimalinteger, the first operand will be assumed to be a<i>date_time</i>operand.Otherwise, the first operand will be assumed to be a<i>file</i>operand.<p></dl></blockquote><h4><a name = "tag_001_014_2301"> </a>STDIN</h4><blockquote>Not used.</blockquote><h4><a name = "tag_001_014_2302"> </a>INPUT FILES</h4><blockquote>None.</blockquote><h4><a name = "tag_001_014_2303"> </a>ENVIRONMENT VARIABLES</h4><blockquote>The following environment variables affect the execution of<i>touch</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><dt><i>TZ</i><dd>Determine the timezone to be used for interpreting the<i>time</i>option-argument(or<i>date_time</i>operand; see above).</dl></blockquote><h4><a name = "tag_001_014_2304"> </a>ASYNCHRONOUS EVENTS</h4><blockquote>Default.</blockquote><h4><a name = "tag_001_014_2305"> </a>STDOUT</h4><blockquote>Not used.</blockquote><h4><a name = "tag_001_014_2306"> </a>STDERR</h4><blockquote>Used only for diagnostic messages.</blockquote><h4><a name = "tag_001_014_2307"> </a>OUTPUT FILES</h4><blockquote>None.</blockquote><h4><a name = "tag_001_014_2308"> </a>EXTENDED DESCRIPTION</h4><blockquote>None.</blockquote><h4><a name = "tag_001_014_2309"> </a>EXIT STATUS</h4><blockquote>The following exit values are returned:<dl compact><dt>0<dd>The utility executed successfully and all requested changes were made.<dt>>0<dd>An error occurred.</dl></blockquote><h4><a name = "tag_001_014_2310"> </a>CONSEQUENCES OF ERRORS</h4><blockquote>Default.</blockquote><h4><a name = "tag_001_014_2311"> </a>APPLICATION USAGE</h4><blockquote>The interpretation of time is taken to be<b>seconds since the Epoch</b>(seethe <b>XBD</b> specification, <a href="../xbd/glossary.html"><b>Glossary</b> </a> ).It should be noted that implementations conforming to the <b>XSH</b> specificationdo not take leap seconds into account when computingseconds since the Epoch.When<i>SS</i><b>=</b>60is used, the resultingtime always refers to 1 plus "seconds since the Epoch"for a time when<i>SS</i><b>=</b>59.<p>Although the<b>-t</b> <i>time</i>option-argument and theobsolescent<i>date_time</i>operand specify values in 1969, the accesstime and modification time fields are defined in terms ofseconds since the Epoch (midnight on 1 January 1970UTC).Therefore, depending on the value of<i>TZ</i>when<i>touch</i>is run, there will never be more than a few valid hours in 1969 and thereneed not be any valid times in 1969.<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 the first operand is aneight- or ten-digit decimal number.A portable script can avoid this problem by using:<pre><code>touch -- file</code></pre>or:<pre><code>touch ./file</code></pre>in this case.</blockquote><h4><a name = "tag_001_014_2312"> </a>EXAMPLES</h4><blockquote>None.</blockquote><h4><a name = "tag_001_014_2313"> </a>FUTURE DIRECTIONS</h4><blockquote>The obsolescent<i>date_time</i>operand may be withdrawn in a future issue.Applications should use the<b>-r</b>or<b>-t</b>options.</blockquote><h4><a name = "tag_001_014_2314"> </a>SEE ALSO</h4><blockquote><i><a href="date.html">date</a></i>,the <b>XSH</b> specification description of<i><a href="../xsh/creat.html">creat()</a></i>,<i><a href="../xsh/time.html">time()</a></i>,<i><a href="../xsh/sysstat.h.html"><sys/stat.h></a></i>.</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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