Advanced Bash−Scripting Guide

Chapter 25. List Constructs
The "and list" and "or list" constructs provide a means of processing a number of commands consecutively.
These can effectively replace complex nested if/then or even case statements.
Chaining together commands
and list
command−1 && command−2 && command−3 && ... command−n
Each command executes in turn provided that the previous command has given a return value of true
(zero). At the first false (non−zero) return, the command chain terminates (the first command
returning false is the last one to execute).
Example 25−1. Using an "and list" to test for command−line arguments
#!/bin/bash
# "and list"
if [ ! −z "$1" ] && echo "Argument #1 = $1" && [ ! −z "$2" ] && echo "Argument #2 = $2"
then
echo "At least 2 arguments passed to script."
# All the chained commands return true.
else
echo "Less than 2 arguments passed to script."
# At least one of the chained commands returns false.
fi
# Note that "if [ ! −z $1 ]" works, but its supposed equivalent,
# if [ −n $1 ] does not. However, quoting fixes this.
# if [ −n "$1" ] works. Careful!
# It is best to always quote tested variables.
# This accomplishes the same thing, using "pure" if/then statements.
if [ ! −z "$1" ]
then
echo "Argument #1 = $1"
fi
if [ ! −z "$2" ]
then
echo "Argument #2 = $2"
echo "At least 2 arguments passed to script."
else
echo "Less than 2 arguments passed to script."
fi
# It's longer and less elegant than using an "and list".
exit 0
Example 25−2. Another command−line arg test using an "and list"
Chapter 25. List Constructs 289