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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 1.76b+"><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="Subshells"HREF="subshells.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"><TABLESUMMARY="Header navigation table"WIDTH="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"ACCESSKEY="P">Prev</A></TD><TDWIDTH="80%"ALIGN="center"VALIGN="bottom">Chapter 19. I/O Redirection</TD><TDWIDTH="10%"ALIGN="right"VALIGN="bottom"><AHREF="subshells.html"ACCESSKEY="N">Next</A></TD></TR></TABLE><HRALIGN="LEFT"WIDTH="100%"></DIV><DIVCLASS="SECT1"><H1CLASS="SECT1"><ANAME="REDIRAPPS"></A>19.3. Applications</H1><P>Clever use of I/O redirection permits parsing and stitching	together snippets of command output (see <AHREF="internal.html#READREDIR">Example 14-7</A>). This permits	 generating report and log files.</P><DIVCLASS="EXAMPLE"><HR><ANAME="LOGEVENTS"></A><P><B>Example 19-12. Logging events</B></P><TABLEBORDER="0"BGCOLOR="#E0E0E0"WIDTH="100%"><TR><TD><PRECLASS="PROGRAMLISTING">   1&nbsp;#!/bin/bash   2&nbsp;# logevents.sh   3&nbsp;# Author: Stephane Chazelas.   4&nbsp;# Used in ABS Guide with permission.   5&nbsp;   6&nbsp;# Event logging to a file.   7&nbsp;# Must be run as root (for write access in /var/log).   8&nbsp;   9&nbsp;ROOT_UID=0     # Only users with $UID 0 have root privileges.  10&nbsp;E_NOTROOT=67   # Non-root exit error.  11&nbsp;  12&nbsp;  13&nbsp;if [ "$UID" -ne "$ROOT_UID" ]  14&nbsp;then  15&nbsp;  echo "Must be root to run this script."  16&nbsp;  exit $E_NOTROOT  17&nbsp;fi    18&nbsp;  19&nbsp;  20&nbsp;FD_DEBUG1=3  21&nbsp;FD_DEBUG2=4  22&nbsp;FD_DEBUG3=5  23&nbsp;  24&nbsp;# === Uncomment one of the two lines below to activate script. ===  25&nbsp;# LOG_EVENTS=1  26&nbsp;# LOG_VARS=1  27&nbsp;  28&nbsp;  29&nbsp;log()  # Writes time and date to log file.  30&nbsp;{  31&nbsp;echo "$(date)  $*" &#62;&#38;7     # This *appends* the date to the file.  32&nbsp;#     ^^^^^^^  command substitution  33&nbsp;                           # See below.  34&nbsp;}  35&nbsp;  36&nbsp;  37&nbsp;  38&nbsp;case $LOG_LEVEL in  39&nbsp; 1) exec 3&#62;&#38;2         4&#62; /dev/null 5&#62; /dev/null;;  40&nbsp; 2) exec 3&#62;&#38;2         4&#62;&#38;2         5&#62; /dev/null;;  41&nbsp; 3) exec 3&#62;&#38;2         4&#62;&#38;2         5&#62;&#38;2;;  42&nbsp; *) exec 3&#62; /dev/null 4&#62; /dev/null 5&#62; /dev/null;;  43&nbsp;esac  44&nbsp;  45&nbsp;FD_LOGVARS=6  46&nbsp;if [[ $LOG_VARS ]]  47&nbsp;then exec 6&#62;&#62; /var/log/vars.log  48&nbsp;else exec 6&#62; /dev/null                     # Bury output.  49&nbsp;fi  50&nbsp;  51&nbsp;FD_LOGEVENTS=7  52&nbsp;if [[ $LOG_EVENTS ]]  53&nbsp;then  54&nbsp;  # exec 7 &#62;(exec gawk '{print strftime(), $0}' &#62;&#62; /var/log/event.log)  55&nbsp;  # Above line fails in versions of Bash more recent than 2.04. Why?  56&nbsp;  exec 7&#62;&#62; /var/log/event.log              # Append to "event.log".  57&nbsp;  log                                      # Write time and date.  58&nbsp;else exec 7&#62; /dev/null                     # Bury output.  59&nbsp;fi  60&nbsp;  61&nbsp;echo "DEBUG3: beginning" &#62;&#38;${FD_DEBUG3}  62&nbsp;  63&nbsp;ls -l &#62;&#38;5 2&#62;&#38;4                             # command1 &#62;&#38;5 2&#62;&#38;4  64&nbsp;  65&nbsp;echo "Done"                                # command2   66&nbsp;  67&nbsp;echo "sending mail" &#62;&#38;${FD_LOGEVENTS}  68&nbsp;# Writes "sending mail" to file descriptor #7.  69&nbsp;  70&nbsp;  71&nbsp;exit 0</PRE></TD></TR></TABLE><HR></DIV></DIV><DIVCLASS="NAVFOOTER"><HRALIGN="LEFT"WIDTH="100%"><TABLESUMMARY="Footer navigation table"WIDTH="100%"BORDER="0"CELLPADDING="0"CELLSPACING="0"><TR><TDWIDTH="33%"ALIGN="left"VALIGN="top"><AHREF="redircb.html"ACCESSKEY="P">Prev</A></TD><TDWIDTH="34%"ALIGN="center"VALIGN="top"><AHREF="index.html"ACCESSKEY="H">Home</A></TD><TDWIDTH="33%"ALIGN="right"VALIGN="top"><AHREF="subshells.html"ACCESSKEY="N">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"ACCESSKEY="U">Up</A></TD><TDWIDTH="33%"ALIGN="right"VALIGN="top">Subshells</TD></TR></TABLE></DIV></BODY></HTML>
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