#!/perl -w
use strict;

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

my $string_index = 0;
my $last_end_point = 0;
foreach my $sub_string (@sub_strings) {
	
	my $string_index = index($string, $sub_string, $string_index);
	die ("Couldn't find string") if $string_index == -1;

	my $overlap = $last_end_point - $string_index;
	if ($overlap > 0) {
		substr($sub_string, 0, $overlap) = '-'x$overlap;
	}
	$last_end_point = $string_index + (length($sub_string));
}
print join(',', @sub_strings);