#!/usr/bin/perl -w
use strict;
use Benchmark;
my $testlarge = "a " x 100000;
my $testsmall = "a b c d e f";
timethese(-10,{
        One   => sub { my ($y) = (split(/\s+/,$testlarge))[0]; },
        Two   => sub { my ($y) = (split(/\s+/,$testsmall))[0]; },
        Three => sub { $testsmall =~ /([^\s]*)\s+/; my $y = $1; },
        Four  => sub { $testlarge =~ /([^\s]*)\s+/; my $y = $1; },
              });

##</code><code>##

Benchmark: running Four, One, Three, Two, each for at least 10 CPU seconds...
      Four: 10 wallclock secs ( 4.55 usr +  5.48 sys = 10.03 CPU) @ 439.88/s (n=4412)
       One: 13 wallclock secs (12.83 usr +  0.07 sys = 12.90 CPU) @  4.88/s (n=63)
     Three: 11 wallclock secs (10.62 usr +  0.00 sys = 10.62 CPU) @ 94938.32/s (n=1008245)
       Two: 10 wallclock secs (10.01 usr +  0.00 sys = 10.01 CPU) @ 67121.98/s (n=671891)