mirror of
https://github.com/flokoe/bash-hackers-wiki.git
synced 2024-11-26 00:03:41 +01:00
73 lines
2.2 KiB
Plaintext
73 lines
2.2 KiB
Plaintext
====== The exec builtin command ======
|
|
|
|
===== Synopsis =====
|
|
<code>exec [-a NAME] [-cl] [COMMAND] [ARG...] [REDIRECTION...]</code>
|
|
|
|
===== 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 [[internals:shell_options#execfail | shell option execfail]] is set ''exec'' returns failure
|
|
* in an interactive shell, ''exec'' returns failure
|
|
|
|
===== Examples =====
|
|
|
|
==== Wrapper around a program ====
|
|
<code 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" "$@"
|
|
</code>
|
|
|
|
==== Open a file as input for the script ====
|
|
<code 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<&-
|
|
</code>
|
|
|
|
==== 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:
|
|
<code bash>
|
|
exec >/var/adm/my.log 2>&1
|
|
|
|
# script continues here...
|
|
</code>
|
|
|
|
===== 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 =====
|
|
* [[syntax:redirection]]
|