The exec built-in replaces the shell process with another external command.

Syntax

  • exec [-cf] [-a name] [command [argument…]]

The exec built-in requires that all options precede operands. It is important so that options to the exec built-in are not confused with options to command. Any command line arguments after command are treated as arguments.

Description

When the exec built-in is executed with command, the shell executes command with arguments in a manner similar to the last step of execution of a simple command. The differences are that command is always treated as an external command ignoring any existing functions and built-ins and that the exec system call that starts the external command is called in the current command execution environment instead of a subshell, replacing the shell process with the new command process.

If the shell is in the POSIXly-correct mode or not interactive, failure in execution of command causes the shell to exit immediately.

If an interactive shell that is not in the POSIXly-correct mode has a stopped job, the shell prints a warning message and refuses to execute command. Once the shell process is replaced with an external command, information about the shell’s jobs is lost, so you will have to resume or kill the stopped jobs by sending signals by hand. To force the shell to execute command regardless, specify the -f (--force) option.

When executed without command, the built-in does nothing. As a side effect, however, redirection applied to the built-in remains in the current command execution environment even after the built-in finished.

Options

-a name
--as=name

Pass name, instead of command, to the external command as its name.

-c
--clear

Pass to the external command only variables that are assigned in the simple command in which the built-in is being executed. Other environment variables are not passed to the command.

-f
--force

Suppress warnings that would prevent command execution.

Operands

command

An external command to be executed.

argument…

Arguments to be passed to the command.

Exit status

If the shell process was successfully replaced with the external command, there is no exit status since the shell process no longer exists.

The exit status is:

  • 127 if the command was not found,

  • 126 if the command was found but could not be executed, and

  • zero if no command was specified.

Notes

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

The POSIX standard defines no options for the exec built-in; the built-in accepts no options in the POSIXly-correct mode.