Applications

	Advanced Bash-Scripting Guide:
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16.3. Applications

Clever use of I/O redirection permits parsing and stitching together snippets of command output (see Example 11- 5). This permits generating report and log files.

Example 16-11. Logging events

#!/bin/bash

#logevents.sh, by Stephane Chazelas.

#Event logging to a file.

#Must be run as root (for write access in /var/log).

ROOT_UID=0	#	Only users with $UID	0 have root privileges.
E_NOTROOT=67	#	Non-root exit error.

if [ "$UID" -ne "$ROOT_UID" ] then

echo "Must be root to run this script." exit $E_NOTROOT

fi

FD_DEBUG1=3

FD_DEBUG2=4

FD_DEBUG3=5

#Uncomment one of the two lines below to activate script.

#LOG_EVENTS=1

#LOG_VARS=1

log() # Writes time and date to log file.

{

echo "$(date) $*" >&7	# This *appends* the date to the file.
	# See below.
}

case $LOG_LEVEL in
1)	exec 3>&2	4> /dev/null 5> /dev/null;;
2)	exec 3>&2	4>&2	5> /dev/null;;
3)	exec 3>&2	4>&2	5>&2;;

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Applications

*) exec 3> /dev/null 4> /dev/null 5> /dev/null;; esac

FD_LOGVARS=6
if [[ $LOG_VARS ]]
then exec 6>> /var/log/vars.log
else exec 6> /dev/null	# Bury output.
fi

FD_LOGEVENTS=7

if [[ $LOG_EVENTS ]] then

#then exec 7 >(exec gawk '{print strftime(), $0}' >> /var/log/event.log)

#Above line will not work in Bash, version 2.04.

exec 7>> /var/log/event.log	# Append to "event.log".
log		# Write time and date.
else exec 7> /dev/null		# Bury output.
fi
echo "DEBUG3: beginning" >&${FD_DEBUG3}
ls -l >&5 2>&4	# command1 >&5 2>&4
echo "Done"		# command2
echo "sending mail" >&${FD_LOGEVENTS}		# Writes "sending mail" to fd #7.
exit 0
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