Bash-Beginners-Guide

The commands after && are only executed when the test proves to be true; this is a shorter way to represent
an if/then/fi structure.
The return code of the function is often used as exit code of the entire script. You'll see a lot of initscripts
ending in something like exit $RETVAL.
11.1.4. Displaying functions
Bash Guide for Beginners
All functions known by the current shell can be displayed using the set built-in without options. Functions are
retained after they are used, unless they are unset after use. The which command also displays functions:
[lydia@cointreau ~] which zless
zless is a function
zless ()
{
zcat "$@" | "$PAGER"
}
[lydia@cointreau ~] echo $PAGER
less
This is the sort of function that is typically configured in the user's shell resource configuration files.
Functions are more flexible than aliases and provide a simple and easy way of adapting the user environment.
Here's one for DOS users:
dir ()
{
ls -F --color=auto -lF --color=always "$@" | less -r
}
11.2. Examples of functions in scripts
11.2.1. Recycling
There are plenty of scripts on your system that use functions as a structured way of handling series of
commands. On some Linux systems, for instance, you will find the /etc/rc.d/init.d/functions
definition file, which is sourced in all init scripts. Using this method, common tasks such as checking if a
process runs, starting or stopping a daemon and so on, only have to be written once, in a general way. If the
same task is needed again, the code is recycled.
You could make your own /etc/functions file that contains all functions that you use regularly on your
system, in different scripts. Just put the line
. /etc/functions
somewhere at the start of the script and you can recycle functions.
Chapter 11. Functions 133