#!/usr/bin/env perl -l

use strict;
use warnings;

my @data = ('X_12_yzAAA', 'X_34_yzBBB', 'X_56_yzCCC', 'X_78_yzAAA',);
my $re = qr{^.+_(\d+)_.+([A-C]{3})$};
my %despatch = (
    AAA => sub { print 'found1 with digits: ', shift },
    BBB => sub { print 'found2 with digits: ', shift },
    CCC => sub { print 'found3 with digits: ', shift },
);

/$re/ && $despatch{$2}->($1) for @data;