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

my $string    = "PHAGEPHAGEPQKREPHAGEPWSQEPHAGEPRDLEPHAGE";
my $substring = "PHAGE";

my $count    =  0;
my $last_pos =  -1;

NAKED:
	{
	$last_pos = index( $string, $substring, $last_pos + 1 );
	last if $last_pos == -1;
	
	print "Found $substring at $last_pos\n";
	$count++;
	redo;
	}
	
print "Found $count instances of $substring\n";

__OUTPUT__
Found PHAGE at 0
Found PHAGE at 5
Found PHAGE at 15
Found PHAGE at 25
Found PHAGE at 35
Found 5 instances of PHAGE