readonly

readonly [variable1 variable2 ...]
readonly -p

Prevent the specified shell variables from being assigned new values. Variables can be accessed (read) but not overwritten. In the Korn shell, the syntax variable=value can assign a new value that cannot be changed. The second form is specific to ksh93.

Option

-p

Print readonly before printing the names and values of read-only variables. This allows saving a list of read-only variables for rereading later.