2.3 KiB
====== 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 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 =====