wiki.bash-hackers.org/commands/builtin/readonly.md

# The readonly builtin command

## Synopsis

    readonly [-p] [-a] [-A] [-f] [NAME[=VALUE] ...]

## Description

The `readonly` builtin command is used to mark variables or functions as
read-only, which means unchangeable. This implies that it can't be unset
anymore. A `readonly` variable may not be redefined in child scopes. A
readonly global may not be redefined as a function local variable.
Simple command environment assignments may not reference readonly
variables.

### Options

| Option | Description                                                                                                            |
|:-------|:-----------------------------------------------------------------------------------------------------------------------|
| `-a`   | refer to normal arrays                                                                                                 |
| `-A`   | refer to associative arrays                                                                                            |
| `-f`   | refer to functions                                                                                                     |
| `-p`   | print all read-only variables or functions, `-a`, `-A` and `-f` can be used to filter. The output is reusable as input |

An argument of `--` disables further option processing.

### Return status

| Status | Reason                         |
|:-------|:-------------------------------|
| 0      | no error                       |
| !=0    | invalid option                 |
| !=0    | invalid combination of options |
| !=0    | a given `NAME` is invalid      |

## Examples

## Portability considerations

- in POSIX(r), only the `-p` option is specified

## See also

- [declare](/commands/builtin/declare.md)