Re: Bug or feature? s/// and the g option

[dsheroh]

I'd guess that it's undefined because, in the final example, the last partial match (B...) fails and apparently clears $1 before doing so. Reversing the order of those lines works without returning the warning:

$test = <<'END';
ABFG
ABCD
END

Edit: I poked at it a little more and seem to have confirmed my theory. If the final B in the data string is not followed by C?[DE], $1 ends up undef, regardless of where that B is.

[Belgarion]

Interesting. So a failed match will clear the $1 variable. I'm still a little stumped by Marco's original example:

$test = <<'END';
XXWY
XXWZ
END

$count = $test =~ s#(XXW?Y)##gi;
print "REMOVED: <<$1>>\nCOUNT: $count\n";

That fails. But remove the "i" in the substitution and $1 is defined. Why would case-insensitive make any difference?
--rjk

[ysth]

AIUI, without the i, before the regex engine proper is entered, there's an optimization that makes it search for an XX followed later by a Y. That optimization rejects a match, and when that happens, it bypasses the bug that's setting $1 to undef. Seems to be fixed for 5.10.0.

[Belgarion]

Ah, thanks for the explanation ysth!
--rjk