I wonder if that could be re-written w/ hash slices?

#!/usr/bin/perl
use strict;
use warnings;
my $sentence = "abxcd zwe rrv";
my $wantedLetters = "tzxv";

my %required;
@required{split //,$wantedLetters}=();
delete @required{split //, $sentence};

if (keys %required) {
   print "required yet missing: ",keys %required,"\n";
   }
else {
   print "all requirements were met!\n";
   }
[download]

Quick test... Yup, that works! Fun...