Advanced Bash−Scripting Guide

Advanced Bash−Scripting Guide
# Something like this might be useful in some contexts.
NO_EXIT=1 # Will enable function definition below.
[[ $NO_EXIT −eq 1 ]] && exit() { true; } # Function definition in an "and−list".
# If $NO_EXIT is 1, declares "exit ()".
# This disables the "exit" builtin by aliasing it to "true".
exit # Invokes "exit ()" function, not "exit" builtin.
# Thanks, S.C.
23.1. Complex Functions and Function Complexities
Functions may process arguments passed to them and return an exit status to the script for further processing.
function_name $arg1 $arg2
The function refers to the passed arguments by position (as if they were positional parameters), that is, $1,
$2, and so forth.
Example 23−2. Function Taking Parameters
#!/bin/bash
# Functions and parameters
DEFAULT=default
# Default param value.
func2 () {
if [ −z "$1" ]
# Is parameter #1 zero length?
then
echo "−Parameter #1 is zero length.−" # Or no parameter passed.
else
echo "−Param #1 is \"$1\".−"
fi
variable=${1−$DEFAULT}
echo "variable = $variable"
# What does
#+ parameter substitution show?
# −−−−−−−−−−−−−−−−−−−−−−−−−−−
# It distinguishes between
#+ no param and a null param.
if [ "$2" ]
then
echo "−Parameter #2 is \"$2\".−"
fi
}
return 0
echo
echo "Nothing passed."
func2
echo
# Called with no params
Chapter 23. Functions 276