#!/usr/bin/env perl -l

use strict;
use warnings;

my $search = 'AAA';
my $offset = length $search;

while (<DATA>) {
    chomp;
    my $last_find_pos = length($_) - $offset;
    my $found_pos = rindex $_, $search, $last_find_pos;

    if ($found_pos == -1) {
        print "'$search' not found in '$_'";
    }
    elsif ($found_pos == $last_find_pos) {
        print "'$search' found at end of '$_'";
    }
    else {
        print "'$search' found before (but not at) end of '$_'";
    }
}

__DATA__
AAAAA
AAAAB
AAABB
AABBB
ABBBB
BBBBB