in reply to Bug or feature? s/// and the g option

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

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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.

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Re^2: Bug or feature? s/// and the g option
by Belgarion (Chaplain) on Oct 14, 2007 at 16:17 UTC
    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";

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    That fails. But remove the "i" in the substitution and $1 is defined. Why would case-insensitive make any difference?
    --rjk
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[d/l]
      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.
[reply]
        Ah, thanks for the explanation ysth!
        --rjk
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