sub test_regex {
    my @array1 = ( "test", "test2", "test2", "test3", "test4", "test4" );
    my @array2 = ( "test", "test", "test2.1", "test4.1", "test4.2", "test4.3" );

    # Create a list of the items in array 1 separated by |
    # The reverse sort is used to keep the longer names to the front of
    # the list, in order to avoid matching 'test' when we could match 'test4'
    my $match_array1 = join('|',reverse sort @array1);

    # Using the 'x' option with regular expressions helps readability, 
    # even in simple cases like this
    my $regex        = qr{
                         ^
                         ($match_array1)
                       }x;


    my %found_one = ();
    foreach my $item2 (@array2) {
        next unless defined $item2;
        if ($item2 =~ /$regex/) {
            $found_one{$1}++;
        }
    }
    return keys %found_one;
}

##</code><code>##

use strict;
use warnings;
use Benchmark qw(cmpthese);
if (0) {
    print "regex: $_\n" for test_regex();
    print "loop:  $_\n" for test_loop();
    exit;
}
cmpthese(1000,{
    loop => \&test_loop,
    regex => \&test_regex,
});


sub test_regex {
    my @array1 = ( "test", "test2", "test2", "test3", "test4", "test4" );
    my @array2 = ( "test", "test", "test2.1", "test4.1", "test4.2", "test4.3" );

    # Create a list of the items in array 1 separated by |
    # The reverse sort is used to keep the longer names to the front of
    # the list, in order to avoid matching 'test' when we could match 'test4'
    my $match_array1 = join('|',reverse sort @array1);

    # Using the 'x' option with regular expressions helps readability, 
    # even in simple cases like this
    my $regex        = qr{
                         ^
                         ($match_array1)
                       }x;


    my %found_one = ();
    foreach my $item2 (@array2) {
        next unless defined $item2;
        if ($item2 =~ /$regex/) {
            $found_one{$1}++;
        }   
    }   
    return keys %found_one;
}
sub test_loop {
    my @array1 = ( "test", "test2", "test2", "test3", "test4", "test4" );
    my @array2 = ( "test", "test", "test2.1", "test4.1", "test4.2", "test4.3" );
    my %found_one = ();

    foreach my $item1 (@array1) {
        foreach my $item2 (@array2) {
            next unless defined $item2;
            if (match_names($item1, $item2)) {
                $found_one{$item1}++;
                last;
            }
        }
    }
    return keys %found_one;

}

sub match_names {
  my ($x,$y) = @_;
  return 1 if ($y =~ /$x/);
  return;
}


##</code><code>##

        Rate  loop regex
loop  1136/s    --  -60%
regex 2857/s  151%    --