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

my $str = "1b22a3d3cab";
my @letters = qw (a b 2 c d);
my @order_found =();
my %seen =();

#UPDATE: don't need the $found variable, oops!
#while (my $found = $str =~ m/([join("",@letters)])/go)
#should have been:
while ($str =~ m/([join("",@letters)])/go)
{
   push (@order_found, $1) unless $seen{$1};
   $seen{$1}++;
}
if (keys %seen != @letters)
{
   print "not all letters found\n";
}
else
{
   print @order_found, "\n"; # prints b2adc
}