mirror of
https://github.com/flokoe/bash-hackers-wiki.git
synced 2024-11-01 14:53:06 +01:00
86 lines
2.2 KiB
Markdown
86 lines
2.2 KiB
Markdown
# 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](/internals/shell_options#execfail) is set `exec`
|
|
returns failure
|
|
- in an interactive shell, `exec` returns failure
|
|
|
|
## Examples
|
|
|
|
### Wrapper around a program
|
|
|
|
``` bash
|
|
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
|
|
|
|
``` bash
|
|
# 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:
|
|
|
|
``` bash
|
|
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](/syntax/redirection)
|