Use of exit status variables (for example, E_NOARGS) clarification needed

cuintilo · 07-10-2018, 09:16 AM

Hello

I've been reading abs-guide after researching some man pages and doing some simple scripts and while after beginning I feel I understand majority of information presented I didn't manage to wrap my thoughts around concept of variables used in examples there.

For example, if you have an exception handler (is it called like this?) which informs that input should contain something and which ends with line

Quote:

exit $E_NOARGS

What does that variable actually do? It's been given value of 65 in the example script, but why that value? Is it just some convention used for this type of exit, since status should still be 'false', yes? I read exit function man page, but it didn't state anything about this matter. Help reaching clarity on the matter is greatly appreciated.

NevemTeve · 07-10-2018, 09:21 AM

> What does that variable actually do?

The variable does nothing, only holds a value.

> It's been given value of 65 in the example script, but why that value?

Because the programmer choose that value. Actually, it could be anything but zero.

> Is it just some convention used for this type of exit, since status should still be 'false', yes?

Nonzero is a more precise term. Zero=Success, Non-zero=Failure

bigearsbilly · 07-10-2018, 10:57 AM

It is information to the caller if it failed or not.
0 is success, > 0 is a clue to the error, maybe 1 is 'not found' 2 is 'not allowed' etc.

In linux it is a mash up of the status and the signal in the exit code.
I set my prompt to show the exit code of the last command:

Code:

$ PS1='$? $ '
0 $ cat flap
cat: flap: No such file or directory
1 $ (exit 99)
99 $ (exit 255)
255 $ (exit 256)
0 $