use warnings;
use strict;

my %barcode_hash = (
    1 => ['AGCTCGTTGTTCGATCCA','GAGAGATAGATGATAGTG','TTTT_CCCC',0],
    2 => ['AGCTCGTTGTTCGATCCA','GAGAGATAGATGATAGTG','TTTT_AAAA',0],
    3 => ['AGCTCGTTGTTCGATCCA','GAGAGATAGATGATAGTG','TTTT_BBBB',0],
    4 => ['AGCTCGTTGTTCGATCCA','GAGAGATAGATGATAGTG','TTTT_AAAA',0],
);

Find_and_Increment ('TTTT_AAAA');
Find_and_Increment ('TTTT_CCCC');
Find_and_Increment ('TTTT_AAAA');

#--------------------
sub Find_and_Increment{
	my ($pair) = @_;

	for my $k (keys %barcode_hash){
       next unless ( my $aref = $barcode_hash{$k} ) -> [2] eq $pair;
       $aref->[3]++;
       print "$pair found at $k, $aref->[3] time(s)\n";
	}
}

##</code><code>##

$ perl search_hash.pl 
TTTT_AAAA found at 4, 1 time(s)
TTTT_AAAA found at 2, 1 time(s)
TTTT_CCCC found at 1, 1 time(s)
TTTT_AAAA found at 4, 2 time(s)
TTTT_AAAA found at 2, 2 time(s)