#!/usr/bin/perl -w
use strict;

my $s = 'one,two,three,four';
my @p;
while(  $s =~ /([^,]+)/g  ) {
    push @p, \substr( $s, pos($s)-length($1), length($1) );
}

print "($$_)" for @p;  print " [$s]\n";

${$p[0]} = 'five';  # Change 'one' to 'five'
${$p[2]} = 'X';     # Change 'three' to 'X'

print "($$_)" for @p;  print " [$s]\n";

print $], $/;
__END__
(one)(two)(three)(four) [one,two,three,four]
(five)(,tw)(X)(r) [five,twoXe,four]
5.012000