use strict;
use warnings;
use Benchmark 'cmpthese';

my $str = ' ' x 1e5;

sub test1 {
    my $s = shift;
    my $copy = substr $str, 1;
    1 while $copy =~ /./g;
    _:
}

sub test2 {
    my $s = shift;
    substr $s, 0, 1, '';
    1 while $s =~ /./g;
    _:
}

cmpthese -1, {
    test1 => sub { test1( $str )},
    test2 => sub { test2( $str )},
};

#             (warning: too few iterations for a reliable count)
#         Rate test2 test1
# test2 2.79/s    --  -93%
# test1 41.0/s 1372%    --