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

my $line = "36,'', NULL, '', 'on', '', 300";
my @tokens = split(/\,\s*/, $line);
foreach (@tokens)
{
   $_ = "''" if $_ eq 'NULL';
   print "$_\n";
}

__END__
36
''
''
'' ## NULL is now an empty string
'on'
''
300