#!perl
use v5.10;
use strict;
use warnings;
use Benchmark qw(:all);

my $results = timethese( 1e6,
  {
    repeat => sub{
      my $t1 = '20090123';
      $t1 =~ /(\d\d\d\d)(\d\d)(\d\d)/;
      my ($y1,$m1,$d1) = ($1,$2,$3);
    },
    range => sub{
      my $t2 = '20090123';
      $t2 =~ /(\d{4})(\d{2})(\d{2})/;
      my ($y2,$m2,$d2) = ($1,$2,$3);
    },
    chkunpk => sub{
      my $t3 = '20090123';
      $t3 =~ m/([0-9]{8})/;
      my ($y3,$m3,$d3) = unpack "A4 A2 A2", $1;
    },
    dirunpk => sub{
      my $t3 = '20090123';
      my ($y4,$m4,$d4) = unpack "A4 A2 A2", $t3;
    },
    isook => sub{
      my $t5 = '20090123';
      $t5 =~ /(....)(..)(..)/;
      my ($y5,$m5,$d5) = ($1,$2,$3);
    },
  } );

cmpthese( $results ) ;

__END__

1st run:

Benchmark: timing 1000000 iterations of chkunpk, dirunpk, isook, range, repeat...
   chkunpk:  4 wallclock secs ( 3.11 usr +  0.00 sys =  3.11 CPU) @ 321646.83/s (n=1000000)
   dirunpk:  2 wallclock secs ( 2.06 usr +  0.00 sys =  2.06 CPU) @ 484966.05/s (n=1000000)
     isook:  1 wallclock secs ( 1.95 usr +  0.00 sys =  1.95 CPU) @ 512032.77/s (n=1000000)
     range:  3 wallclock secs ( 2.16 usr +  0.00 sys =  2.16 CPU) @ 463821.89/s (n=1000000)
    repeat:  2 wallclock secs ( 1.97 usr +  0.00 sys =  1.97 CPU) @ 508130.08/s (n=1000000)
            Rate chkunpk   range dirunpk  repeat   isook
chkunpk 321647/s      --    -31%    -34%    -37%    -37%
range   463822/s     44%      --     -4%     -9%     -9%
dirunpk 484966/s     51%      5%      --     -5%     -5%
repeat  508130/s     58%     10%      5%      --     -1%
isook   512033/s     59%     10%      6%      1%      --

2nd run:

Benchmark: timing 1000000 iterations of chkunpk, dirunpk, isook, range, repeat...
   chkunpk:  2 wallclock secs ( 3.11 usr +  0.00 sys =  3.11 CPU) @ 321646.83/s (n=1000000)
   dirunpk:  3 wallclock secs ( 2.05 usr +  0.00 sys =  2.05 CPU) @ 488519.79/s (n=1000000)
     isook:  2 wallclock secs ( 1.98 usr +  0.00 sys =  1.98 CPU) @ 504032.26/s (n=1000000)
     range:  1 wallclock secs ( 2.11 usr +  0.00 sys =  2.11 CPU) @ 474158.37/s (n=1000000)
    repeat:  3 wallclock secs ( 2.06 usr +  0.00 sys =  2.06 CPU) @ 484966.05/s (n=1000000)
            Rate chkunpk   range  repeat dirunpk   isook
chkunpk 321647/s      --    -32%    -34%    -34%    -36%
range   474158/s     47%      --     -2%     -3%     -6%
repeat  484966/s     51%      2%      --     -1%     -4%
dirunpk 488520/s     52%      3%      1%      --     -3%
isook   504032/s     57%      6%      4%      3%      --