Bash-Beginners-Guide

Of course you could have opened your mail program to check the results; this is just to demonstrate that the
script sends a decent mail with "To:", "Subject:" and "From:" header lines.
Many more examples using case statements can be found in your system's init script directory. The startup
scripts use start and stop cases to run or stop system processes. A theoretical example can be found in the
next section.
7.3.2. Initscript example
Bash Guide for Beginners
Initscripts often make use of case statements for starting, stopping and querying system services. This is an
excerpt of the script that starts Anacron, a daemon that runs commands periodically with a frequency
specified in days.
case "$1" in
start)
start
;;
stop)
stop
;;
status)
status anacron
;;
restart)
stop
start
;;
condrestart)
if test "x`pidof anacron`" != x; then
stop
start
fi
;;
*)
echo $"Usage: $0 {start|stop|restart|condrestart|status}"
exit 1
esac
The tasks to execute in each case, such as stopping and starting the daemon, are defined in functions, which
are partially sourced from the /etc/rc.d/init.d/functions file. See Chapter 11 for more
explanation.
7.4. Summary
In this chapter we learned how to build conditions into our scripts so that different actions can be undertaken
upon success or failure of a command. The actions can be determined using the if statement. This allows you
to perform arithmetic and string comparisons, and testing of exit code, input and files needed by the script.
A simple if/then/fi test often preceeds commands in a shell script in order to prevent output generation, so that
the script can easily be run in the background or through the cron facility. More complex definitions of
conditions are usually put in a case statement.
Chapter 7. Conditional statements 92