cc: [email protected]
Subject: Re: [ast-users] [ksh93] How to return $? from a function when $? > 256
--------
> For example, following code is very common in scripts:
>
> ### CODE BEGIN ###
> function debug
> {
> return
> }
>
> function runcmd
> {
> typeset cmd=$1
> typeset rc
>
> debug "+++ $cmd"
> eval "$cmd"
> rc=$?
> if (( rc )); then
> debug "+++ $cmd failed with $rc"
> else
> debug "+++ $cmd succeeded"
> fi
>
> return $rc
> }
>
> runcmd '/usr/bin/sleep 15'
> echo $?
> ### CODE END ###
>
> The problem is when the command is killed by a signal, we cannot return the
> correct $? (> 256) from the runcmd() function. Bash does not has this
> problem since $? is equal to 128+signal when a command is killed.
>
> (attachment 1 18/1063 text/html "1.att")
>
This is a bug that is already on my list for ksh93v.
The problem with using exit codes of 128+signo (as the Bourne shell did),
is that users can use these exit normal codes. For historical reasons the
standard allows 128+signo, bug 256+signo is safer.
User who do 'exit 267' must get 11 since only the lower eight bits
are valid.
However, the shell should treat exit $? specially since it means
propogate an exit code. For a program it means exit with
this signal by sending the signal to the current process.
For a function, it has to preserve the 256. The key is to
differentiate
exit 267
and
exit $?
The former will become ($?&0xff) the latter, $?.
David Korn
[email protected]
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