Benchmark: timing 10000 iterations of abigail, grinder, posixguy, roger...
   abigail: 55 wallclock secs (51.42 usr +  0.12 sys = 51.54 CPU) @ 194.02/s (n=10000)
   grinder:  1 wallclock secs ( 0.60 usr +  0.00 sys =  0.60 CPU) @ 16666.67/s (n=10000)
  posixguy:  1 wallclock secs ( 0.96 usr +  0.00 sys =  0.96 CPU) @ 10416.67/s (n=10000)
     roger:  1 wallclock secs ( 0.61 usr +  0.00 sys =  0.61 CPU) @ 16393.44/s (n=10000)

##</code><code>##

#!/usr/bin/perl -w

use strict;
use Benchmark;

my @data = qw{1949 1950 1951 1999 2000 2001 2010 2049 2050 2051 2102 22102 19534 19080 20010};

sub grinder() {
        my $foo = 0;
        foreach( @data ) {
            chomp;
            ++$foo if (/^(19[5-9]\d|20([0-4]\d|50))$/);
        }
        return $foo;
}
sub roger() {
        my $foo = 0;
        foreach (@data) {
                chomp;
                ++$foo if (/^(?:19|20)(?:(?:(?<=19)[5-9]|(?<=20)[0-4])[0-9]|50)$/x);
        }
        return $foo;
}
sub posixguy() {
        my $foo = 0;
        foreach (@data) {
                chomp;
                ++$foo if (/^(19[5-9]\d)|(20([0-4]\d)|50)$/);
        }
        return $foo;
}
sub abigail() {
        my $foo = 0;
        foreach (@data) {
                chomp;
                local $" = "|";
                ++$foo if (/^(?:@{[1950 .. 2050]})$/);
        }
        return $foo;
}

timethese(10000, {grinder=>'grinder()', roger=>'roger()', posixguy=>'posixguy()', abigail=>'abigail()'});