Exec built-in

The exec built-in replaces the current shell process with an external utility invoked by treating the specified operands as a command. Without operands, the built-in makes redirections applied to it permanent in the current shell environment.

Synopsis

exec [name [arguments...]]

Description

When invoked with operands, the exec built-in replaces the currently executing shell process with a new process image, regarding the operands as command words to start the external utility. The first operand identifies the utility, and the other operands are passed to the utility as command-line arguments.

Without operands, the built-in does not start any utility. Instead, it makes any redirections performed in the calling simple command permanent in the current shell environment. (This is done even if there are operands, but the effect can be observed only when the utility cannot be invoked and the shell does not exit.)

Options

POSIX defines no options for the exec built-in.

The following non-portable options are yet to be implemented:

• --as
• --clear
• --cloexec
• --force
• --help

Operands

The operands are treated as a command to start an external utility. If any operands are given, the first is the utility name, and the others are its arguments.

If the utility name contains a slash character, the shell will treat it as a path to the utility. Otherwise, the shell will search $PATH for the utility.

Errors

If the name operand is given, the named utility cannot be invoked, and the shell is not interactive, the current shell process will exit with an error.

Exit status

If the external utility is invoked successfully, it replaces the shell executing the built-in, so there is no exit status of the built-in. If the built-in fails to invoke the utility, the exit status will be 126. If there is no utility matching the first operand, the exit status will be 127.

If no operands are given, the exit status will be 0.

Examples

To make the current shell process run echo:

$ exec echo "Hello, World!"
Hello, World!

Note that the echo executed here is not the built-in, but the external utility found in the $PATH. The shell process is replaced by the echo process, so you don’t return to the shell prompt after the command.

See Persistent redirections for examples of using the exec built-in to make redirections permanent.

Compatibility

The exec built-in is part of POSIX.1-2024.