#!/usr/bin/perl
use warnings;
use strict;
use Slurp;
use Data::Dumper;

my $strings = join '|', qw( AB AC AD AE FG );
my $counts;
for my $file (glob ('File/*')) {
    $counts->{$_}++ foreach (Slurp($file) =~ m/($strings)/gms);
}
print Dumper($counts);