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kill builtin argument parsing



Hello there,

I recently mistakenly used arguments for the /bin/kill binary with the zsh kill builtin and noticed something strange that I think should be improved.

The command line I used was:
kill -1 -- <any pid>
which ends up killing the current Zsh process.

This is because the pid valid argument check at Src/builtin.c:2572 uses isanum() that just asserts that all characters in the string are either '-' or a digit. When the string "--" is parsed as a digit with atoi() in Src/jobs.c:2572 it returns '0' which is passed to kill(2) syscall.

I'm not sure whether to suggest changing the isanum() function, or the check in bin_kill() that relies on it. I would personally change the isanum() function, as a cursory reading of the two places it's used appear to not require this particular behaviour (the other place it's used in Src/jobs.c:2193 doesn't appear to have any negative consequences either way), but the comment above this isanum() function clearly shows it was a known behaviour, so there may be a reason I'm missing.

Either way I think the behaviour is surprising enough and possible enough to be worth changing.


Cheers

MM



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