Learning Linux Shell Scripting - Second Edition

Working with read-only variables

During shell scripting, we may need a few variables, which cannot be modified. This may be needed for security reasons. We can declare variables as read-only by using the following read-only command:

$ readonly currency=Dollars

Let's try to remove the variable:

$ unset currencybash: unset: currency: cannot unset: readonly variable

If we try to change or remove the read-only variable in the script, it will give the following error:

#!/bin/bash 
AUTHOR="Ganesh Naik" 
readonly AUTHOR 
AUTHOR="John" 

This will produce the following result:

/bin/sh: AUTHOR: This variable is read only.

Another technique is as follows:

declare  -r  variable=1 
echo "variable=$variable" 
(( var1++ )) 

The output after execution of the script ...