Learning Linux Shell Scripting

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 using following command read-only:

The usage is as follows:

$ readonly currency=Dollars

Let's try to remove the variable:

$ unset currency
bash: unset: currency: cannot unset: readonly variable

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

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

This would produce the following result:

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

Another technique:

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

Output after execution of the script:

line ...