Skip to content

The exec builtin command¶

Synopsis¶

exec [-a NAME] [-cl] [COMMAND] [ARG...] [REDIRECTION...]

Description¶

The exec builtin command is used to

replace the shell with a given program (executing it, not as new process)
set redirections for the program to execute or for the current shell

If only redirections are given, the redirections affect the current shell without executing any program.

Options¶

Option	Description
`-a NAME`	Passes `NAME` as zeroth argument for the program to be executed
`-c`	Execute the program with an empty (cleared) environment
`-l`	Prepends a dash (`-`) to the zeroth argument of the program to be executed, similar to what the `login` program does

Exit status¶

on redirection errors it returns 1, otherwise 0
on exec failures:
- a non-interactive shell terminates; if the shell option execfail is set exec returns failure
- in an interactive shell, exec returns failure

Examples¶

Wrapper around a program¶

myprog=/bin/ls
echo "This is the wrapper script, it will exec $myprog"

# do some vodoo here, probably change the arguments etc.
# well, stuff a wrapper is there for

exec "$myprog" "$@"

Open a file as input for the script¶

# open it
exec 3< input.txt

# for example: read one line from the file(-descriptor)
read -u 3 LINE
# or
read LINE <&3

# finally, close it
exec 3<&-

Overall script logfile¶

To redirect the whole stdout and stderr of the shell or shellscript to a file, you can use the exec builtin command:

exec >/var/adm/my.log 2>&1

# script continues here...

Portability considerations¶

*POSIX(r) specifies error code ranges:
  * if ''exec'' can't find the program to execute, the error code shall be 126
  * on a redirection error, the error code shall be between 1 and 125
* the ''-a NAME'' option appeared in Bash 4.2-alpha
* POSIX(r) does **not** specify any options for ''exec'' (like ''-c'', ''-l'', ''-a NAME'').

See also¶

redirection