mirror of
https://github.com/flokoe/bash-hackers-wiki.git
synced 2024-11-01 14:53:06 +01:00
141 lines
9.2 KiB
Markdown
141 lines
9.2 KiB
Markdown
# Exit Status
|
|
|
|
- exit code
|
|
- return status
|
|
|
|
## Purpose
|
|
|
|
The exit status is a numeric value that is returned by a program to the
|
|
calling program or shell. In C programs, this is represented by the
|
|
return value of the `main()` function or the value you give to
|
|
`exit(3)`. The only part of the number that matters are the least
|
|
significant 8 bits, which means there are only values from 0 to 255.
|
|
|
|
In the shell, every operation generates an exit status (return status),
|
|
even if no program is called. An example for such an operation is a
|
|
redirection.
|
|
|
|
The parameter to the
|
|
|
|
- `exit` (exit the shell/script)
|
|
- `return` (return from a function)
|
|
|
|
builtin commands serve the purpose of giving the exit status to the
|
|
calling component.
|
|
|
|
This - and only this - makes it possible to determinate the success or
|
|
failure of an operation. For scripting, always set exit codes.
|
|
|
|
## Values
|
|
|
|
The code is a number between 0 and 255, where the part from 126 to 255
|
|
is reserved to be used by the Bash shell directly or for special
|
|
purposes, like reporting a termination by a signal:
|
|
|
|
Code Description
|
|
--------- ------------------------------------------------------------------------------------------------------------------------------------------------------------
|
|
0 success
|
|
1-255 failure (in general)
|
|
126 the requested command (file) can\'t be executed (but was found)
|
|
127 command (file) not found
|
|
128 according to ABS it\'s used to report an invalid argument to the exit builtin, but I wasn\'t able to verify that in the source code of Bash (see code 255)
|
|
128 + N the shell was terminated by the signal N (also used like this by various other programs)
|
|
255 wrong argument to the exit builtin (see code 128)
|
|
|
|
The lower codes 0 to 125 are not reserved and may be used for whatever
|
|
the program likes to report. A value of **0 means successful**
|
|
termination, a value **not 0 means unsuccessful** termination. This
|
|
behavior (== 0, != 0) is also what Bash reacts on in some code flow
|
|
control statements like `if` or `while`.
|
|
|
|
## Portability
|
|
|
|
Tables of shell behavior involving non-portable side-effects or common
|
|
bugs with exit statuses. Note heirloom doesn\'t support pipeline
|
|
negation (`! pipeline`).
|
|
|
|
### Misc
|
|
|
|
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|
|
test bash\ bash\ zsh 5.0.2\ ksh93\ mksh\ posh\ dash\ busybox\ heirloom\
|
|
4.2.45 (POSIX) (emulate ksh) 93v- 2013-03-18 R44 2013/02/24 0.11 0.5.7.3 1.2.1 050706
|
|
----------------------------------------------------------------------------------------------------- -------- --------- --------------- ----------------- ---------------- ------- --------- ---------- -----------
|
|
`` :; : `false` `echo $? >&2` `` 1 1 1 1 0 0 0 0 1
|
|
|
|
`false; eval; echo $?` 0 0 0 0 0 1 0 1 0
|
|
|
|
`` x=`false` eval echo \$? `` 1 1 1 1 0 0 0 0 1
|
|
|
|
`` eval echo \$? <&0`false` `` 1 1 1 1 0 0 0 0 1
|
|
|
|
`while :; do ! break; done; echo $?` 1 1 1 1 0 0 1 1 \-
|
|
|
|
[discussion](https://lists.gnu.org/archive/html/bug-bash/2010-09/msg00009.html)`false; : | echo $?` 1 1 1 0 1 1 1 1 0
|
|
|
|
`` (exit 2); for x in "`exit 3`"; do echo $?; done `` 3 3 3 3 2 2 0 0 3
|
|
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|
|
|
|
### functions
|
|
|
|
Measuring side-effects during the function call, during return, and
|
|
transparency of the return builtin.
|
|
|
|
-------------------------------------------------------------------------------------------------------------------------------------------
|
|
test bash bash\ zsh\ ksh93 mksh posh dash busybox heirloom
|
|
(POSIX) (emulate ksh)
|
|
-------------------------------------------------------- ------ --------- --------------- ------- ------ ------ ------ --------- ----------
|
|
`` f() { echo $?; }; :; f `false` `` 1 1 1 1 0 0 0 0 1
|
|
|
|
`f() { return; }; false; f; echo $?` 1 1 1 0 1 1 1 1 1
|
|
|
|
`f() { return $?; }; false; f; echo $?` 1 1 1 1 1 1 1 1 1
|
|
|
|
`f() { ! return; }; f; echo $?` 0 0 1 0 0 0 1 1 \-
|
|
|
|
`f() { ! return; }; false; f; echo $?` 1 1 0 0 1 1 0 0 \-
|
|
|
|
`` f() { return; }; x=`false` f; echo $? `` 1 1 1 1 0 0 0 0 0
|
|
|
|
`` f() { return; }; f <&0`false`; echo $? `` 1 1 1 1 0 0 0 0 1
|
|
|
|
`` f() { x=`false` return; }; f; echo $? `` 1 1 1 0 0 0 0 0 1
|
|
|
|
`` f() { return <&0`false`; }; f; echo $? `` 1 1 1 0 0 0 0 0 1
|
|
|
|
`` f() { x=`false` return <&0`false`; }; f; echo $? `` 1 1 1 1 0 0 0 0 1
|
|
-------------------------------------------------------------------------------------------------------------------------------------------
|
|
|
|
### case..esac
|
|
|
|
Statuses measured within the command and after, with matching and
|
|
non-matching patterns.
|
|
|
|
-------------------------------------------------------------------------------------------------------------------------------------------------
|
|
test bash bash\ zsh\ ksh93 mksh posh dash busybox heirloom
|
|
(POSIX) (emulate ksh)
|
|
-------------------------------------------------------------- ------ --------- --------------- ------- ------ ------ ------ --------- ----------
|
|
`(exit 2); case x in x) echo $?;; esac` 2 2 0 2 2 2 0 0 2
|
|
|
|
`` (exit 2); case `exit 3`x in x) echo $?;; esac `` 3 3 0 3 2 2 0 0 3
|
|
|
|
`` (exit 2); case x in `exit 4`x) echo $?;; esac `` 4 4 4 4 2 2 0 0 4
|
|
|
|
`` (exit 2); case `exit 3`x in `exit 4`x) echo $?;; esac `` 4 4 4 4 2 2 0 0 4
|
|
|
|
`(exit 2); case x in x);; esac; echo $?` 0 0 0 0 0 0 0 0 2
|
|
|
|
`(exit 2); case x in "");; esac; echo $?` 0 0 0 0 0 0 0 0 2
|
|
|
|
`` (exit 2); case `exit 3`x in x);; esac; echo $? `` 0 0 0 3 0 0 0 0 3
|
|
|
|
`` (exit 2); case `exit 3`x in "");; esac; echo $? `` 0 0 0 3 0 0 0 0 3
|
|
|
|
`` (exit 2); case x in `exit 4`x);; esac; echo $? `` 0 0 0 4 0 0 0 0 4
|
|
|
|
`` (exit 2); case x in `exit 4`);; esac; echo $? `` 0 0 4 4 0 0 0 0 4
|
|
|
|
`` (exit 2); case `exit 3`x in `exit 4`);; esac; echo $? `` 0 0 4 4 0 0 0 0 4
|
|
|
|
`` (exit 2); case `exit 3`x in `exit 4`x);; esac; echo $? `` 0 0 0 4 0 0 0 0 4
|
|
-------------------------------------------------------------------------------------------------------------------------------------------------
|