use strict;
use warnings;

my $regex = qr/ ([^,]+) (?=\Z|,) /x;
my $var   = 'abcd,ef,,ghijkl,mnop';

print "$1\n" while $var =~ /$regex/g;

##</code><code>##

18:27 >perl 827_SoPW.pl
abcd
ef
ghijkl
mnop

18:27 >

##</code><code>##

use strict;
use warnings;

my $var     = 'abcd,ef,,ghijkl,mnop';
my @matches = split /,/, $var;

$_ && print "$_\n" for @matches;