Mark one or more variables or functions as read-only.
Syntax
readonly [-apf] [name[=word] ...]
Key
-a Treat each name as an array variable.
-p Print a list of all readonly names (This is the default)
-f Mark shell functions corresponding to the names as read-only.
The given names are marked readonly and the values of these names can not be changed by subsequent assignment.
If the -f option is given, then functions corresponding to the names are so marked.
If no arguments are given, or if '-p' is given, a list of all readonly names is printed.
The '-a' option means to treat each name as an array variable.
An argument of '--' disables further option processing.
If a variable name is followed by =word, the value of the variable is set to word.
The return status is 0 unless an invalid option is encountered, one of the names is not a valid shell variable name, or -f is supplied with a name that is not a function.
This is a BASH shell builtin, to display your local syntax from the bash prompt type: help [r]eadonly
“The universe is like a safe to which there is a combination. But the combination is locked up in the safe” ~ Peter De Vries
set - Set a shell variable = value