That "last" made you miss entries. To make you realize your mistake, here is the code you can compare with: (But this is not the solution to go for speed. Say the two arrays are of size n and m. In the worst case, this solution costs n*m, whereas use a hash (for DB) will only cost the size of the input data)

use strict;
use warnings 'all';

my @DB = qw(AB1/1 AB1/5 AB2/5);
my @Input = qw(AB1/1 AB1/2 AB1/5 AB1/6 AB1/9 AB2/2 AB2/5 AB2/6 AB2/9 A
+B2/13);
for my $InputData (@Input) {
    my $found;
    for my $DBData (@DB) {
        if ($DBData eq $InputData) {
            $found = 1;
            last;
        } 
    }
    print "$InputData : " . ($found?" ":" Not") . "Found\n";
}
[download]

Which prints:

AB1/1 :  Found
AB1/2 :  NotFound
AB1/5 :  Found
AB1/6 :  NotFound
AB1/9 :  NotFound
AB2/2 :  NotFound
AB2/5 :  Found
AB2/6 :  NotFound
AB2/9 :  NotFound
AB2/13 :  NotFound
[download]

Update: removed the extra brace liverpole found. Copy and Paste... Thanks!