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Related to https://github.com/flokoe/bash-hackers-wiki/issues/10
86 lines
2.3 KiB
Markdown
86 lines
2.3 KiB
Markdown
# The exec builtin command
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## Synopsis
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exec [-a NAME] [-cl] [COMMAND] [ARG...] [REDIRECTION...]
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## Description
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The `exec` builtin command is used to
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- **replace** the shell with a given program (executing it, **not as
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new process**)
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- set redirections for the program to execute or for the current shell
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If only redirections are given, the redirections affect the current
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shell without executing any program.
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### Options
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Option Description
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----------- ----------------------------------------------------------------------------------------------------------------------
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`-a NAME` Passes `NAME` as zeroth argument for the program to be executed
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`-c` Execute the program with an empty (cleared) environment
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`-l` Prepends a dash (`-`) to the zeroth argument of the program to be executed, similar to what the `login` program does
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### Exit status
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- on redirection errors it returns 1, otherwise 0
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- on exec failures:
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- a non-interactive shell terminates; if the [shell option
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execfail](../../internals/shell_options.md#execfail) is set `exec`
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returns failure
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- in an interactive shell, `exec` returns failure
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## Examples
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### Wrapper around a program
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``` bash
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myprog=/bin/ls
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echo "This is the wrapper script, it will exec $myprog"
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# do some vodoo here, probably change the arguments etc.
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# well, stuff a wrapper is there for
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exec "$myprog" "$@"
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```
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### Open a file as input for the script
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``` bash
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# open it
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exec 3< input.txt
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# for example: read one line from the file(-descriptor)
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read -u 3 LINE
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# or
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read LINE <&3
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# finally, close it
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exec 3<&-
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```
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### Overall script logfile
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To redirect the whole `stdout` and `stderr` of the shell or shellscript
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to a file, you can use the `exec` builtin command:
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``` bash
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exec >/var/adm/my.log 2>&1
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# script continues here...
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```
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## Portability considerations
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*POSIX(r) specifies error code ranges:
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* if ''exec'' can't find the program to execute, the error code shall be 126
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* on a redirection error, the error code shall be between 1 and 125
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* the ''-a NAME'' option appeared in Bash 4.2-alpha
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* POSIX(r) does **not** specify any options for ''exec'' (like ''-c'', ''-l'', ''-a NAME'').
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## See also
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- [redirection](../../syntax/redirection.md)
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