When the line return 0 if ($2 !~ /(d|p|t)/); is executed, $2 is undef because in the previous regex matching (the one in the line just above it!) has only one pair of parentheses. Use something like this (untested):

sub test {
   my $a = shift;
   my ($first, $second, $third, $fourth, $fifth) = $a =~ /(.)(.)(.)(..
+)(.+)/;

   return 0 if ($first  !~ /(a)/);
   return 0 if ($second !~ /(d|p|t)/);
   return 0 if ($third  !~ /(a|h|r|s|t)/);
   return 0 if ($fourth !~ /(aw|er|dd|cb|aa)/);
}
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