#!/perl -w
use strict;

my $string = "abcdefghijklmnopqrstuvwxyz";
my @sub_strings = ('cdef', 'efghij', 'klmno', 'mnopqrst');

my $string_index = 0;
my $last_end_point = index($string, $sub_strings[0]) + length($sub_strings[0]);

foreach my $sub_array_index (1..$#sub_strings) {

	my $string_index = index($string, $sub_strings[$sub_array_index], $string_index);
	my $overlap = $last_end_point - $string_index;

	# if there's an overlap replace from the front of current string, and the
	# end of the previous string
	if ($overlap > 0) {
		substr($sub_strings[$sub_array_index], 0, $overlap) = '-'x$overlap;
		substr($sub_strings[$sub_array_index-1], -$overlap, $overlap) = '-'x$overlap;
	}

	$last_end_point = $string_index + length($sub_strings[$sub_array_index]);
}