#!/usr/bin/perl
use strict;
use warnings;

my $string = 'every occurrence of a substring in a string';
my $char = 'st';
my $offset = 0;

my $result = index($string, $char, $offset);

while ($result != -1) {

        print "Found $char at $result\n";

        $offset = $result + 1;
        $result = index($string, $char, $offset);

}