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''.
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