# Readonly built-in

The readonly built-in makes variables and functions read-only.

## Syntax

- `readonly [-pxX] [name[=value]…]`

- `readonly -f[p] [name…]`

## Description

The readonly built-in is equivalent to the typeset built-in with the `-gr` option.

## Notes

The readonly built-in is a special built-in.

The POSIX standard defines the `-p` option only; other options cannot be used in the POSIXly-correct mode. The POSIX does not allow using the option together with operands.

In the POSIXly-correct mode, the following variables cannot be made readonly:

- `LINENO`

- `OLDPWD`

- `OPTARG`

- `OPTIND`

- `PWD`