use strict;
use warnings;

use Benchmark qw( cmpthese );

my $string = '1234 this is the remaining string';

cmpthese( -5, {
                unpack => sub { unpack( 'A4xA*', $string ) },
                regex  => sub { $string =~ m[(\d+)\s+(.*)$] },
                split  => sub { split( /(\d+)\s+/, $string, 2 ) },
              } );