Hey guys,
I was hacking around and reading the transcript for japhy's regex book, and I found some weird behavior.

It started when I found out that you could use whitespace after the m, so long as the whitespace was followed by a word character.

$str =~ m TpatternTi;
[download]

Yes its ugly, and probably a bad idea but I thought it might make for a funky piece to an obfu. So I started playing around:

# the only obfu'd part of this code would be the regex
# which fails anyway so nevermind the obfu
# more concerned with the behavior
$str = "foobar fOObar";
$x   = qr/(foo)/i;
print $1 while ($str =~ m _${x}_g);
print "\n";
# prints 'foofOO\n' to STDOUT - fine

$str = "foobar fOObar";
$x   = "(foo)";
print $1 while ($str =~ m _${x}_g);
print "\n";
# prints 'foo\n' to STDOUT - also fine

# this is where it gets weird
# and of course the part I most badly wanted to work
$str = "foobar fOObar";
$_   = qr/(foo)/i;
print $1 while ($str =~ m _${_}_g);
print "\n";
# throws error:
# Missing right bracket at az.pl line 17, within pattern
[download]

Okay, line 17 is the last line of the script and everything else is commented out so I'm 99.9% sure its no glitch in my code. And the bracket is definitely there so what gives?

At first I thought that maybe there was no interpolation performed if you used the whitespace+word character delimiter, but it works fine with $x

Any ideas?

BTW, it doesn't look particularly confusing after all, but I'd still like to know what's happening here ;0).

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Amel