Bash - Readonly Buitlin (Constant variable and function)

About

The given names are marked readonly; the values of these names may not be changed by subsequent assignment.

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Syntax

readonly [-apf] [name[=word] ...]

where:

• -f set also the functions corresponding to the names read-only
• -a restricts the variables to arrays.
• -p prints a list of all readonly names. The -p option causes output to be displayed in a format that may be reused as input.
• [name[=word] …] The value of the variable is set to word.

Without options, a list of all readonly names is printed.

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.