Re: PATCH: test for trap EXIT fix.

[Peter Stephenson <pws@xxxxxxx>]

Bart Schaefer wrote:
> Can you explain to me why the subshell exits without ever leaving the
> function scope?  Why doesn't it just exit from a forked copy of the
> function scope?

There's special handling in the exec function hierarchy, starting with the
`exiting' flag to execlist.  The key chunk of code is this in execcmd(),
around line 2365 of exec.c

		/* If we're forked (and we should be), no need to return */
		DPUTS(last1 != 1 && !forked, "BUG: not exiting?");
		execlist(state, 0, 1);
                                   ^ `exiting' flag

That means we execute the list of command, and when we get to the end, exit
the shell.  I think this is correct --- I don't think we have any business
leaving the function scope for a subshell contained entirely inside a
function.

At least, that's certainly true if you compare what happens when you drop
off the end of a subshell list with what happens when you drop off the end
of a current shell list.  If you compare calling `exit' in the two, the
behaviour is different, but that's not the typical case for a subshell list.

We may be able to do some special tricks with `exiting' at the end of
execlist(), making sure we don't exit too early from lower down in that
case (because of the optimization for a final command to be exec'd if
there's nothing left to do).  Then we just execute any top level EXIT trap
which has been left to us.

-- 
Peter Stephenson <pws@xxxxxxx>                  Software Engineer
CSR Ltd., Science Park, Milton Road,
Cambridge, CB4 0WH, UK                          Tel: +44 (0)1223 392070


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