enable

Enable or disable shell built-in commands.

Synopsis

enable [-a] [-dnps] [-f filename] [name ...]

Description

Disable one or more built-in commands.
Enable one or more built-in commands.
Directly call an external command with the same name as a disabled built-in, found in the $PATH.
Print all built-in commands, whether disabled or not.
Print enabled built-in commands.
Print disabled built-in commands.
Print enabled POSIX special built-in commands.
Print disabled POSIX special built-in commands.
Print all POSIX special built-in commands.
Load built-in commands from a dynamic library.
Remove built-in commands loaded from a dynamic library.

Options

-a    Print all built-in commands, whether disabled or not.
-d    Remove built-in commands loaded from a dynamic library.
-n    Disable built-in commands or show disabled built-in commands.
-p    Print built-in commands in a reusable format.
-s    Display only enabled POSIX special built-in commands.
-f    Load built-in commands from a dynamic library.
-ns   Print disabled POSIX special built-in commands.
-as   Print all POSIX special built-in commands, whether disabled or not.

Parameters

filename: The dynamic library filename.

name (optional): Built-in command(s). Multiple names can be specified.

Return Value

enable returns success unless name is not a built-in command or an error occurs.

Examples

# POSIX special built-ins
# Assuming no built-ins are disabled
# Disable two POSIX special built-ins
enable -n set source
# Print disabled POSIX special built-ins
enable -ns
# Print all POSIX special built-ins
enable -as
# Print enabled POSIX special built-ins
enable -s

# Assuming no built-ins are disabled
# Disable one or more built-in commands
enable -n echo pwd
# Print all built-in commands
enable -a
# Print enabled built-in commands
enable
# Print disabled built-in commands
enable -n
# Enable one or more built-in commands
enable pwd

Q&A

Q: Where are the demonstrations for -f, -d, and -p?

A: Regarding -f and -d, suitable examples haven't been found yet. If you have better examples, feel free to submit a pull request. For the -p option, there seems to be no visible difference in output; you can compare enable -p | cat -A and enable | cat -A to check for invisible characters.

Q: Can I disable enable itself? Can I still enable/disable built-ins after that?

A: Yes, you can disable it. However, once disabled, you cannot use it to enable or disable any built-in commands until it is re-enabled (which usually requires a new shell session).

Note

When a Linux shell command is executed, the shell always looks for the command in its built-ins first. If found, it executes it. If not, it searches through the paths specified in the $PATH environment variable. It might seem like there's no way to override a shell built-in with a user-defined command. Fortunately, the enable command allows us to do exactly that.

Regarding command priority, refer to the "Note" section of the builtin command.

When the built-in echo is not disabled, to call the external echo command, you must use the full path like /usr/bin/echo.

When echo is disabled, the priority becomes: Function > External Command If no echo function exists, the external command will be called.

This is a bash built-in command. For more help, use the help command.