$ths = ' this is a   string';
$i = split(/\s/,$ths);
print "$i\n";

##</code><code>##

$_ = ' this is a   string';
my @words = split " ";
print scalar @words, "\n";

# or you could go for this version :-)

$_ = ' this is a   string';
my $words =()= /(\S+)/g;
print $words, "\n";