If you ever wonder what something matched, you can use

my $at = $-[0];
my $matched = substr($test, $at, $+[0]-$at);
warn(Matched "$matched" at $at\n");
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Alternatively, you could pass the argument -Meval=debug to perl. (e.g. perl -Mre=debug script.pl). It produces a detailed (i.e. long) report of all regexp activities.

References:

• @- and @+ are documented in perlvar.
• -Mre=debug adds use re 'debug'; to your program. See re.