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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><HTML><HEAD><TITLE>Applications</TITLE><METANAME="GENERATOR"CONTENT="Modular DocBook HTML Stylesheet Version 1.57"><LINKREL="HOME"TITLE="Advanced Bash-Scripting Guide"HREF="index.html"><LINKREL="UP"TITLE="I/O Redirection"HREF="io-redirection.html"><LINKREL="PREVIOUS"TITLE="Redirecting Code Blocks"HREF="redircb.html"><LINKREL="NEXT"TITLE="Here Documents"HREF="here-docs.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="redircb.html">Prev</A></TD><TDWIDTH="80%"ALIGN="center"VALIGN="bottom">Chapter 16. I/O Redirection</TD><TDWIDTH="10%"ALIGN="right"VALIGN="bottom"><AHREF="here-docs.html">Next</A></TD></TR></TABLE><HRALIGN="LEFT"WIDTH="100%"></DIV><DIVCLASS="SECT1"><H1CLASS="SECT1"><ANAME="REDIRAPPS">16.3. Applications</A></H1><P>Clever use of I/O redirection permits parsing and stitching	together snippets of command output (see <AHREF="internal.html#READREDIR">Example 11-7</A>). This permits	 generating report and log files.</P><DIVCLASS="EXAMPLE"><HR><ANAME="LOGEVENTS"></A><P><B>Example 16-12. Logging events</B></P><TABLEBORDER="0"BGCOLOR="#E0E0E0"WIDTH="100%"><TR><TD><PRECLASS="PROGRAMLISTING">   1&nbsp;#!/bin/bash   2&nbsp;# logevents.sh, by Stephane Chazelas.   3&nbsp;   4&nbsp;# Event logging to a file.   5&nbsp;# Must be run as root (for write access in /var/log).   6&nbsp;   7&nbsp;ROOT_UID=0     # Only users with $UID 0 have root privileges.   8&nbsp;E_NOTROOT=67   # Non-root exit error.   9&nbsp;  10&nbsp;  11&nbsp;if [ "$UID" -ne "$ROOT_UID" ]  12&nbsp;then  13&nbsp;  echo "Must be root to run this script."  14&nbsp;  exit $E_NOTROOT  15&nbsp;fi    16&nbsp;  17&nbsp;  18&nbsp;FD_DEBUG1=3  19&nbsp;FD_DEBUG2=4  20&nbsp;FD_DEBUG3=5  21&nbsp;  22&nbsp;# Uncomment one of the two lines below to activate script.  23&nbsp;# LOG_EVENTS=1  24&nbsp;# LOG_VARS=1  25&nbsp;  26&nbsp;  27&nbsp;log()  # Writes time and date to log file.  28&nbsp;{  29&nbsp;echo "$(date)  $*" &#62;&#38;7     # This *appends* the date to the file.  30&nbsp;                              # See below.  31&nbsp;}  32&nbsp;  33&nbsp;  34&nbsp;  35&nbsp;case $LOG_LEVEL in  36&nbsp; 1) exec 3&#62;&#38;2         4&#62; /dev/null 5&#62; /dev/null;;  37&nbsp; 2) exec 3&#62;&#38;2         4&#62;&#38;2         5&#62; /dev/null;;  38&nbsp; 3) exec 3&#62;&#38;2         4&#62;&#38;2         5&#62;&#38;2;;  39&nbsp; *) exec 3&#62; /dev/null 4&#62; /dev/null 5&#62; /dev/null;;  40&nbsp;esac  41&nbsp;  42&nbsp;FD_LOGVARS=6  43&nbsp;if [[ $LOG_VARS ]]  44&nbsp;then exec 6&#62;&#62; /var/log/vars.log  45&nbsp;else exec 6&#62; /dev/null               # Bury output.  46&nbsp;fi  47&nbsp;  48&nbsp;FD_LOGEVENTS=7  49&nbsp;if [[ $LOG_EVENTS ]]  50&nbsp;then  51&nbsp;  # then exec 7 &#62;(exec gawk '{print strftime(), $0}' &#62;&#62; /var/log/event.log)  52&nbsp;  # Above line will not work in Bash, version 2.04.  53&nbsp;  exec 7&#62;&#62; /var/log/event.log        # Append to "event.log".  54&nbsp;  log                                      # Write time and date.  55&nbsp;else exec 7&#62; /dev/null                  # Bury output.  56&nbsp;fi  57&nbsp;  58&nbsp;echo "DEBUG3: beginning" &#62;&#38;${FD_DEBUG3}  59&nbsp;  60&nbsp;ls -l &#62;&#38;5 2&#62;&#38;4                       # command1 &#62;&#38;5 2&#62;&#38;4  61&nbsp;  62&nbsp;echo "Done"                                # command2   63&nbsp;  64&nbsp;echo "sending mail" &#62;&#38;${FD_LOGEVENTS}   # Writes "sending mail" to fd #7.  65&nbsp;  66&nbsp;  67&nbsp;exit 0</PRE></TD></TR></TABLE><HR></DIV></DIV><DIVCLASS="NAVFOOTER"><HRALIGN="LEFT"WIDTH="100%"><TABLEWIDTH="100%"BORDER="0"CELLPADDING="0"CELLSPACING="0"><TR><TDWIDTH="33%"ALIGN="left"VALIGN="top"><AHREF="redircb.html">Prev</A></TD><TDWIDTH="34%"ALIGN="center"VALIGN="top"><AHREF="index.html">Home</A></TD><TDWIDTH="33%"ALIGN="right"VALIGN="top"><AHREF="here-docs.html">Next</A></TD></TR><TR><TDWIDTH="33%"ALIGN="left"VALIGN="top">Redirecting Code Blocks</TD><TDWIDTH="34%"ALIGN="center"VALIGN="top"><AHREF="io-redirection.html">Up</A></TD><TDWIDTH="33%"ALIGN="right"VALIGN="top">Here Documents</TD></TR></TABLE></DIV></BODY></HTML>
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