exec — Run a command and open, close, or copy the file descriptors

Format

exec [–a name] [command_line]

tcsh shell: exec command

Description

The command_line argument for exec specifies a command line for another command. exec runs this command without creating a new process. Some people picture this action as overlaying the command on top of the currently running shell. Thus, when the command exits, control returns to the parent of the shell.

Input and output redirections are valid in command_line. You can change the input and output descriptors of the shell by giving only input and output redirections in the command. For example:

exec 2>errors

redirects the standard error stream to errors in all subsequent commands ran by the shell.

If you do not specify command_line, exec returns a successful exit status.

In the tcsh shell, exec executes the specified command in place of the current shell. See tcsh — Invoke a C shell.

Options

–a name: The shell passes name as the zero'th argument (argv[0]) to command_line. –a name can be used to replace the current shell with a new login shell, by specifying name as a shell with a prefix of a dash (–).

Examples

To replace the current shell process with a new login shell (which will run the login profiles), specify:

exec -a -sh /bin/sh

Usage notes

exec is a special built-in shell command.

Localization

exec uses the following localization environment variables:

LANG
LC_ALL
LC_MESSAGES
NLSPATH

See Localization for more information.

Exit values

If you specify command_line, exec does not return to the shell. Instead, the shell exits with the exit status of command_line or one of the following exit status values:

1–125: A redirection error occurred.
126: The command in command_line was found, but it was not an executable utility.
127: The given command_line could not be run because the command could not be found in the current PATH environment.

If you did not specify command_line, exec returns with an exit value of zero.

Portability

POSIX.2, X/Open Portability Guide, UNIX systems.

Related information

sh, tcsh