perl -le '$_ = "\n"; print /^$/'
1

##</code><code>##

#        1         2         3         4         5         6
#23456789012345678901234567890123456789012345678901234567890123456789
map{$n=$o=$_;for$c(@_){$n+=s/$c//}/^$/&&push@{$w[$n]},$o}<D>;@{pop@w}

##</code><code>##

#!/usr/bin/perl -wT
use strict;

my @arr             = ("\n","dog\n","cat\n");
my $patternmatch    = 0;
my $underscorematch = 0;

/^$/ && $patternmatch++    for @arr;
$_   || $underscorematch++ for @arr;

print "Patternmatch    = $patternmatch\n";     # <==  prints 1
print "Underscorematch = $underscorematch\n";  # <==  prints 0