Benchmark confirms: 
use strict;
use Benchmark;

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);
    },
  } );

my $results2 = timethese( 1e6,
  {
    range2 => sub{
      my $t3 = '20090123';
      $t3 =~ /(\d{4})(\d{2})(\d{2})/;
      my ($y3,$m3,$d3) = ($1,$2,$3);
    },
    repeat2 => sub{
      my $t4 = '20090123';
      $t4 =~ /(\d\d\d\d)(\d\d)(\d\d)/;
      my ($y4,$m4,$d4) = ($1,$2,$3);
    },
  }
);
__END__

Benchmark: timing 1000000 iterations of range, repeat...
     range:  2 wallclock secs ( 1.69 usr +  0.00 sys =  1.69 CPU) @ 59
+2417.06/s (n=1000000)
    repeat:  2 wallclock secs ( 1.53 usr +  0.00 sys =  1.53 CPU) @ 65
+3167.86/s (n=1000000)
Benchmark: timing 1000000 iterations of range2, repeat2...
    range2:  2 wallclock secs ( 1.70 usr +  0.00 sys =  1.70 CPU) @ 58
+6854.46/s (n=1000000)
   repeat2:  0 wallclock secs ( 1.53 usr +  0.00 sys =  1.53 CPU) @ 65
+3167.86/s (n=1000000)

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In reply to Re^2: better (faster) way of writing regexp by keszler
in thread better (faster) way of writing regexp by jodaka

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