use strict;
use warnings;
use Benchmark qw(cmpthese);

my $key = 'x';
my $str = ("\n  The quick brown frog jumped over the lazy dog" x 10000) . "\n x";

cmpthese (-10,
        {
        sol => \&sol,
        nl => \&nl,
        lb => \&lb,
        }
    );


sub sol {$str =~ /^ \s* $key /mx;}
sub nl {$str =~ /\n \s* $key /mx;}
sub lb {$str =~ /(?<![^\n]) \s* $key /mx;}


       Rate     sol      lb      nl
sol 0.316/s      --    -99%   -100%
lb   35.0/s  10997%      --    -92%
nl    441/s 139470%   1158%      --