Mastering Linux Shell Scripting - Second Edition

Setting defaults

Using either the test command or the brackets, we can provide default values for variables, including command-line parameters. Taking the hello4.sh script we worked with earlier, we can modify it and set the name parameter if it is zero bytes:

#!/bin/bashname=$1[ -z $name ] && name="Anonymous"echo "Hello $name"exit 0

This code is functional but it is our choice how we code in the default value. We can, alternatively, assign a default value directly to the parameter. Consider the following command, where a default assignment is made directly:

name=${1-"Anonymous"}

In bash, this is known as parameter substitution and can be written in the following pseudo-code:

${parameter-default}

Wherever a variable (parameter) has not been ...