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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><HTML><HEAD><TITLE>Time / Date Commands</TITLE><METANAME="GENERATOR"CONTENT="Modular DocBook HTML Stylesheet Version 1.57"><LINKREL="HOME"TITLE="Advanced Bash-Scripting Guide"HREF="index.html"><LINKREL="UP"TITLE="External Filters, Programs and Commands"HREF="external.html"><LINKREL="PREVIOUS"TITLE="Complex Commands"HREF="moreadv.html"><LINKREL="NEXT"TITLE="Text Processing Commands"HREF="textproc.html"><METAHTTP-EQUIV="Content-Style-Type"CONTENT="text/css"><LINKREL="stylesheet"HREF="common/kde-common.css"TYPE="text/css"><METAHTTP-EQUIV="Content-Type"CONTENT="text/html; charset=iso-8859-1"><METAHTTP-EQUIV="Content-Language"CONTENT="en"><LINKREL="stylesheet"HREF="common/kde-localised.css"TYPE="text/css"TITLE="KDE-English"><LINKREL="stylesheet"HREF="common/kde-default.css"TYPE="text/css"TITLE="KDE-Default"></HEAD><BODYCLASS="SECT1"BGCOLOR="#FFFFFF"TEXT="#000000"LINK="#AA0000"VLINK="#AA0055"ALINK="#AA0000"STYLE="font-family: sans-serif;"><DIVCLASS="NAVHEADER"><TABLEWIDTH="100%"BORDER="0"CELLPADDING="0"CELLSPACING="0"><TR><THCOLSPAN="3"ALIGN="center">Advanced Bash-Scripting Guide: An in-depth exploration of the art of shell scripting</TH></TR><TR><TDWIDTH="10%"ALIGN="left"VALIGN="bottom"><AHREF="moreadv.html">Prev</A></TD><TDWIDTH="80%"ALIGN="center"VALIGN="bottom">Chapter 12. External Filters, Programs and Commands</TD><TDWIDTH="10%"ALIGN="right"VALIGN="bottom"><AHREF="textproc.html">Next</A></TD></TR></TABLE><HRALIGN="LEFT"WIDTH="100%"></DIV><DIVCLASS="SECT1"><H1CLASS="SECT1"><ANAME="TIMEDATE">12.3. Time / Date Commands</A></H1><DIVCLASS="VARIABLELIST"><P><B><ANAME="TDLISTING1"></A>Time/date and timing</B></P><DL><DT><ANAME="DATEREF"></A><BCLASS="COMMAND">date</B></DT><DD><P>Simply invoked, <BCLASS="COMMAND">date</B> prints the date and time to <TTCLASS="FILENAME">stdout</TT>. Where this command gets interesting is in its formatting and parsing options.</P><DIVCLASS="EXAMPLE"><HR><ANAME="EX51"></A><P><B>Example 12-10. Using <BCLASS="COMMAND">date</B></B></P><TABLEBORDER="0"BGCOLOR="#E0E0E0"WIDTH="90%"><TR><TD><PRECLASS="PROGRAMLISTING"> 1 #!/bin/bash 2 # Exercising the 'date' command 3 4 echo "The number of days since the year's beginning is `date +%j`." 5 # Needs a leading '+' to invoke formatting. 6 # %j gives day of year. 7 8 echo "The number of seconds elapsed since 01/01/1970 is `date +%s`." 9 # %s yields number of seconds since "UNIX epoch" began, 10 #+ but how is this useful? 11 12 prefix=temp 13 suffix=$(date +%s) # The "+%s" option to 'date' is GNU-specific. 14 filename=$prefix.$suffix 15 echo $filename 16 # It's great for creating "unique" temp filenames, 17 #+ even better than using $$. 18 19 # Read the 'date' man page for more formatting options. 20 21 exit 0</PRE></TD></TR></TABLE><HR></DIV><P>The <TTCLASS="OPTION">-u</TT> option gives the UTC (Universal Coordinated Time).</P><P> <TABLEBORDER="0"BGCOLOR="#E0E0E0"WIDTH="90%"><TR><TD><PRECLASS="SCREEN"> <TTCLASS="PROMPT">bash$ </TT><TTCLASS="USERINPUT"><B>date</B></TT> <TTCLASS="COMPUTEROUTPUT">Fri Mar 29 21:07:39 MST 2002</TT> <TTCLASS="PROMPT">bash$ </TT><TTCLASS="USERINPUT"><B>date -u</B></TT> <TTCLASS="COMPUTEROUTPUT">Sat Mar 30 04:07:42 UTC 2002</TT> </PRE></TD></TR></TABLE> </P><P><ANAME="DATERANDREF"></A></P><P>The <BCLASS="COMMAND">date</B> command has quite a number of output options. For example <TTCLASS="OPTION">%N</TT> gives the nanosecond portion of the current time. One interesting use for this is to generate six-digit random integers. <TABLEBORDER="0"BGCOLOR="#E0E0E0"WIDTH="90%"><TR><TD><PRECLASS="PROGRAMLISTING"> 1 date +%N | sed -e 's/000$//' -e 's/^0//' 2 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 3 # Strip off leading and trailing zeroes, if present.</PRE></TD></TR></TABLE> </P><P>There are many more options (try <BCLASS="COMMAND">man date</B>). <TABLEBORDER="0"BGCOLOR="#E0E0E0"WIDTH="90%"><TR><TD><PRECLASS="PROGRAMLISTING"> 1 date +%j 2 # Echoes day of the year (days elapsed since January 1). 3 4 date +%k%M 5 # Echoes hour and minute in 24-hour format, as a single digit string. 6 7 8 9 # The 'TZ' parameter permits overriding the default time zone. 10 date # Mon Mar 28 21:42:16 MST 2005 11 TZ=EST date # Mon Mar 28 23:42:16 EST 2005 12 # Thanks, Frank Kannemann and Pete Sjoberg, for the tip. 13 14 15 SixDaysAgo=$(date --date='6 days ago') 16 OneMonthAgo=$(date --date='1 month ago') # Four weeks back (not a month). 17 OneYearAgo=$(date --date='1 year ago')</PRE></TD></TR></TABLE></P><P>See also <AHREF="special-chars.html#EX58">Example 3-4</A>.</P></DD><DT><BCLASS="COMMAND">zdump</B></DT><DD><P>Time zone dump: echoes the time in a specified time zone.</P><P> <TABLEBORDER="0"BGCOLOR="#E0E0E0"WIDTH="90%"><TR><TD><PRECLASS="SCREEN"> <TTCLASS="PROMPT">bash$ </TT><TTCLASS="USERINPUT"><B>zdump EST</B></TT> <TTCLASS="COMPUTEROUTPUT">EST Tue Sep 18 22:09:22 2001 EST</TT> </PRE></TD></TR></TABLE> </P></DD><DT><ANAME="TIMREF"></A><BCLASS="COMMAND">time</B></DT><DD><P>Outputs very verbose timing statistics for executing a command.</P><P><TTCLASS="USERINPUT"><B>time ls -l /</B></TT> gives something like this:<TABLEBORDER="0"BGCOLOR="#E0E0E0"WIDTH="90%"><TR><TD><PRECLASS="SCREEN"> <TTCLASS="COMPUTEROUTPUT">0.00user 0.01system 0:00.05elapsed 16%CPU (0avgtext+0avgdata 0maxresident)k 0inputs+0outputs (149major+27minor)pagefaults 0swaps</TT></PRE></TD></TR></TABLE> </P><P>See also the very similar <AHREF="internal.html#TIMESREF">times</A> command in the previous section.</P><DIVCLASS="NOTE"><TABLECLASS="NOTE"WIDTH="90%"BORDER="0"><TR><TDWIDTH="25"ALIGN="CENTER"VALIGN="TOP"><IMGSRC="common/note.png"HSPACE="5"ALT="Note"></TD><TDALIGN="LEFT"VALIGN="TOP"><P>As of <AHREF="bash2.html#BASH2REF">version 2.0</A> of Bash, <BCLASS="COMMAND">time</B> became a shell reserved word, with slightly altered behavior in a pipeline.</P></TD></TR></TABLE></DIV></DD><DT><ANAME="TOUCHREF"></A><BCLASS="COMMAND">touch</B></DT><DD><P>Utility for updating access/modification times of a file to current system time or other specified time, but also useful for creating a new file. The command <TTCLASS="USERINPUT"><B>touch zzz</B></TT> will create a new file of zero length, named <TTCLASS="FILENAME">zzz</TT>, assuming that <TTCLASS="FILENAME">zzz</TT> did not previously exist. Time-stamping empty files in this way is useful for storing date information, for example in keeping track of modification times on a project. </P><DIVCLASS="NOTE"><TABLECLASS="NOTE"WIDTH="90%"BORDER="0"><TR><TDWIDTH="25"ALIGN="CENTER"VALIGN="TOP"><IMGSRC="common/note.png"HSPACE="5"ALT="Note"></TD><TDALIGN="LEFT"VALIGN="TOP"><P>The <BCLASS="COMMAND">touch</B> command is equivalent to <TTCLASS="USERINPUT"><B>: >> newfile</B></TT> or <TTCLASS="USERINPUT"><B>>> newfile</B></TT> (for ordinary files).</P></TD></TR></TABLE></DIV></DD><DT><ANAME="ATREF"></A><BCLASS="COMMAND">at</B></DT><DD><P>The <BCLASS="COMMAND">at</B> job control command executes a given set of commands at a specified time. Superficially, it resembles <AHREF="system.html#CRONREF">cron</A>, however, <BCLASS="COMMAND">at</B> is chiefly useful for one-time execution of a command set.</P><P><TTCLASS="USERINPUT"><B>at 2pm January 15</B></TT> prompts for a set of commands to execute at that time. These commands should be shell-script compatible, since, for all practical purposes, the user is typing in an executable shell script a line at a time. Input terminates with a <AHREF="special-chars.html#CTLDREF">Ctl-D</A>.</P><P>Using either the <TTCLASS="OPTION">-f</TT> option or input redirection (<SPANCLASS="TOKEN"><</SPAN>), <BCLASS="COMMAND">at</B> reads a command list from a file. This file is an executable shell script, though it should, of course, be noninteractive. Particularly clever is including the <AHREF="extmisc.html#RUNPARTSREF">run-parts</A> command in the file to execute a different set of scripts.</P><P> <TABLEBORDER="0"BGCOLOR="#E0E0E0"WIDTH="90%"><TR><TD><PRECLASS="SCREEN"> <TTCLASS="PROMPT">bash$ </TT><TTCLASS="USERINPUT"><B>at 2:30 am Friday < at-jobs.list</B></TT> <TTCLASS="COMPUTEROUTPUT">job 2 at 2000-10-27 02:30</TT> </PRE></TD></TR></TABLE> </P></DD><DT><BCLASS="COMMAND">batch</B></DT><DD><P>The <BCLASS="COMMAND">batch</B> job control command is similar to <BCLASS="COMMAND">at</B>, but it runs a command list when the system load drops below <TTCLASS="LITERAL">.8</TT>. Like <BCLASS="COMMAND">at</B>, it can read commands from a file with the <TTCLASS="OPTION">-f</TT> option.</P></DD><DT><BCLASS="COMMAND">cal</B></DT><DD><P>Prints a neatly formatted monthly calendar to <TTCLASS="FILENAME">stdout</TT>. Will do current year or a large range of past and future years.</P></DD><DT><BCLASS="COMMAND">sleep</B></DT><DD><P>This is the shell equivalent of a wait loop. It pauses for a specified number of seconds, doing nothing. It can be useful for timing or in processes running in the background, checking for a specific event every so often (polling), as in <AHREF="debugging.html#ONLINE">Example 29-6</A>. <TABLEBORDER="0"BGCOLOR="#E0E0E0"WIDTH="90%"><TR><TD><PRECLASS="PROGRAMLISTING"> 1 sleep 3 # Pauses 3 seconds.</PRE></TD></TR></TABLE> </P><DIVCLASS="NOTE"><TABLECLASS="NOTE"WIDTH="90%"BORDER="0"><TR><TDWIDTH="25"ALIGN="CENTER"VALIGN="TOP"><IMGSRC="common/note.png"HSPACE="5"ALT="Note"></TD><TDALIGN="LEFT"VALIGN="TOP"><P>The <BCLASS="COMMAND">sleep</B> command defaults to seconds, but minute, hours, or days may also be specified. <TABLEBORDER="0"BGCOLOR="#E0E0E0"WIDTH="90%"><TR><TD><PRECLASS="PROGRAMLISTING"> 1 sleep 3 h # Pauses 3 hours!</PRE></TD></TR></TABLE> </P></TD></TR></TABLE></DIV><DIVCLASS="NOTE"><TABLECLASS="NOTE"WIDTH="90%"BORDER="0"><TR><TDWIDTH="25"ALIGN="CENTER"VALIGN="TOP"><IMGSRC="common/note.png"HSPACE="5"ALT="Note"></TD><TDALIGN="LEFT"VALIGN="TOP"><P>The <AHREF="system.html#WATCHREF">watch</A> command may be a better choice than <BCLASS="COMMAND">sleep</B> for running commands at timed intervals.</P></TD></TR></TABLE></DIV></DD><DT><BCLASS="COMMAND">usleep</B></DT><DD><P><ICLASS="EMPHASIS">Microsleep</I> (the <SPANCLASS="QUOTE">"u"</SPAN> may be read as the Greek <SPANCLASS="QUOTE">"mu"</SPAN>, or micro- prefix). This is the same as <BCLASS="COMMAND">sleep</B>, above, but <SPANCLASS="QUOTE">"sleeps"</SPAN> in microsecond intervals. It can be used for fine-grain timing, or for polling an ongoing process at very frequent intervals.</P><P> <TABLEBORDER="0"BGCOLOR="#E0E0E0"WIDTH="90%"><TR><TD><PRECLASS="PROGRAMLISTING"> 1 usleep 30 # Pauses 30 microseconds.</PRE></TD></TR></TABLE> </P><P>This command is part of the Red Hat <ICLASS="EMPHASIS">initscripts / rc-scripts</I> package.</P><DIVCLASS="CAUTION"><TABLECLASS="CAUTION"WIDTH="90%"BORDER="0"><TR><TDWIDTH="25"ALIGN="CENTER"VALIGN="TOP"><IMGSRC="common/caution.png"HSPACE="5"ALT="Caution"></TD><TDALIGN="LEFT"VALIGN="TOP"><P>The <BCLASS="COMMAND">usleep</B> command does not provide particularly accurate timing, and is therefore unsuitable for critical timing loops.</P></TD></TR></TABLE></DIV></DD><DT><BCLASS="COMMAND">hwclock</B>, <BCLASS="COMMAND">clock</B></DT><DD><P>The <BCLASS="COMMAND">hwclock</B> command accesses or adjusts the machine's hardware clock. Some options require root privileges. The <TTCLASS="FILENAME">/etc/rc.d/rc.sysinit</TT> startup file uses <BCLASS="COMMAND">hwclock</B> to set the system time from the hardware clock at bootup.</P><P>The <BCLASS="COMMAND">clock</B> command is a synonym for <BCLASS="COMMAND">hwclock</B>.</P></DD></DL></DIV></DIV><DIVCLASS="NAVFOOTER"><HRALIGN="LEFT"WIDTH="100%"><TABLEWIDTH="100%"BORDER="0"CELLPADDING="0"CELLSPACING="0"><TR><TDWIDTH="33%"ALIGN="left"VALIGN="top"><AHREF="moreadv.html">Prev</A></TD><TDWIDTH="34%"ALIGN="center"VALIGN="top"><AHREF="index.html">Home</A></TD><TDWIDTH="33%"ALIGN="right"VALIGN="top"><AHREF="textproc.html">Next</A></TD></TR><TR><TDWIDTH="33%"ALIGN="left"VALIGN="top">Complex Commands</TD><TDWIDTH="34%"ALIGN="center"VALIGN="top"><AHREF="external.html">Up</A></TD><TDWIDTH="33%"ALIGN="right"VALIGN="top">Text Processing Commands</TD></TR></TABLE></DIV></BODY></HTML>⌨️ 快捷键说明
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