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

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# 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
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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)
- [unset](../../commands/builtin/unset.md)