#!/usr/bin/perl

use strict;
use warnings;

my $x = "0.01 NaN 2.30 4.44";

# the following works as desired
my $r1 = qr/([Na0-9\.\-\+]+)\s+
	    ([Na0-9\.\-\+]+)\s+
	    ([Na0-9\.\-\+]+)\s+
	    ([Na0-9\.\-\+]+)/x;

my ($d, $e, $f, $g) = ($x =~ m/$r1/x );
print qq($d, $e, $f, $g\n);


# the following finds the first number twice
my $r2 = qr/(?=(([Na0-9\.\-\+]+)\s*)){4}/x;

($d, $e, $f, $g) = ($x =~ m/$r2/x );
print qq($d, $e, $f, $g\n);

# the following finds a null prior to the first item
my $r3 = qr/((?=([Na0-9\.\-\+]+)\s*){4})/x;

($d, $e, $f, $g) = ($x =~ m/$r3/x );
print qq($d, $e, $f, $g\n);

exit(0);