# surround all uppercase characters in the passed parameter with *'s
# and all lowercase characters with _'s
# (modifies parameter in-place)
sub transmogrify {
   my $string = $_[0];
   $string =~ s/([A-Z])/*$1*/g;
   $string =~ s/([a-z])/_$1_/g;
   $_[0] = $string;
   return;
}

$text = "I met this guy, and he looked like he might have been a hat check clerk at an ice rink, which in fact, he turned out to be.  Let X = X.";
transmogrify($text);
print $text;