#!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);
    },
    substr => sub{
      my $t2 = '20090123';
      my $year =substr ($t2,0,4); 
      my $mon = substr ($t2,4,2);
      my $day = substr ($t2,6,2); 
    },
    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__
output:
Benchmark: timing 1000000 iterations of chkunpk, dirunpk, isook, range, repeat, substr...
   chkunpk:  4 wallclock secs ( 5.05 usr +  0.00 sys =  5.05 CPU) @ 
198137.51/s (n=1000000)
   dirunpk:  2 wallclock secs ( 3.31 usr +  0.00 sys =  3.31 CPU) 
@ 301841.23/s (n=1000000)
     isook:  3 wallclock secs ( 3.08 usr +  0.00 sys =  3.08 CPU) @ 
324886.29/s (n=1000000)
     range:  4 wallclock secs ( 3.23 usr +  0.00 sys =  3.23 CPU) @ 
309214.59/s (n=1000000)
    repeat:  4 wallclock secs ( 3.03 usr +  0.00 sys =  3.03 CPU) @ 
329924.12/s (n=1000000)
    substr:  2 wallclock secs ( 1.22 usr +  0.00 sys =  1.22 CPU) @ 
820344.54/s (n=1000000)
            Rate chkunpk dirunpk   range   isook  repeat  substr
chkunpk 198138/s      --    -34%    -36%    -39%    -40%    -76%
dirunpk 301841/s     52%      --     -2%     -7%     -9%    -63%
range   309215/s     56%      2%      --     -5%     -6%    -62%
isook   324886/s     64%      8%      5%      --     -2%    -60%
repeat  329924/s     67%      9%      7%      2%      --    -60%
substr  820345/s    314%    172%    165%    153%    149%      --