Ola Lundqvist wrote: > > `perldoc -f do` says: > > | If "do" cannot read the file, it returns undef and sets $! to the > > | error. If "do" can read the file but cannot compile it, it returns > > | undef and sets an error message in [EMAIL PROTECTED] If the file is > > | successfully compiled, "do" returns the value of the last > > | expression evaluated. > > > > Thus relying on $! and $@ is officially sanctioned. > > I can not see that. It do not say anything about the $! or $@ when the > expression return true. It only tell that they are set when it returns > false. > > The above statements formalized: > If X return undef and set $! > if Y return undef and set $@ > if Z return $lastexpr > > I can not see anything about > if return true, set $! = 0, set $@ = 0; > > It may be so that it do that and I did some test code that verifies > that. However I do not want to rely on undocumented features too much > if there are documented features that I can rely on.
You're right, and it even actually says (in `perldoc perlvar`) that $!
does NOT get set to 0 if there is no failure. Perhaps you could
explicitly set $! to 0 before the do() call, though?
About $@, I'm certain that it gets set to "" if the file could be read and
compiled successfully.
> > I think the "check whether do() returns true" idiom is a remnant from
> > old times when Perl didn't know exceptions ($@).
>
> This is the result of the test code:
>
> Condition return $! $@
> --------------------------------------
> Read error undef string ""
> Syntax error undef "" string
> No statements undef "" ""
> last 0 0 "" ""
> last 1 1 "" ""
>
> The "" above could also be undef, but I did not have the time to check
> that now.
>
> But this is from my perl version. In your case for "No statements" the
> value for $! and $@ was ^I.
Maybe this is a syslog oddity? I've never seen $! or $@ getting set
to "^I" ("\t"), so I don't think this is their actual value.
> I can provide some testing code to you if you want so we can determine
> the table above for your perl version.
I doubt it would be any different with Perl 5.8.8, which is what I'm
running.
Well, we could try setting $! to 0 before the do() call and checking
($! || $@) afterwards. If that doesn't work, then the debarchiver
man-page would have to explain that there needs to be a final, true-
valued statement in every config file.
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