$ perl -MBenchmark=cmpthese -le 'my $a; $_ = "abcdefghi"; cmpthese( 2_000_000, { "01 \$&" => sub { /def/; $a = $& } } )'
           Rate 01 $&
01 $& 1025641/s    --
$ perl -MBenchmark=cmpthese -le 'my $a; $_ = "abcdefghi"; cmpthese( 2_000_000, { "02 substr" => sub { /def/; $a = substr( $_, $-[0], $+[0] - $-[0] ) }, "03 paren" => sub { /(def)/; $a = $1 } } )'
               Rate 02 substr  03 paren
02 substr  116822/s        --      -89%
03 paren  1098901/s      841%        --