mifflin,
This is what you asked for, but not the way I would do it:

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

my $str = "this is a string";
print pop @{[split(/\s/, $str)]};
[download]

I have never had a need to do this, but I would probably do:

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

my $str = "this is a string";
print $str =~ /\s(\w+)$/;
[download]

Cheers - L~R