for( 30, 300, 3000, 30000 ) { 
    $s = 'x'x$_ . 'reg exp' . 'x'x$_; 
    cmpthese -1, { 
        REGEX => q[ $x = $s =~ /reg exp/;], 
        INDEX => q[ $x = index $s, 'reg exp';] 
    };
};;

           Rate INDEX REGEX
INDEX 1956298/s    --  -19%
REGEX 2425347/s   24%    --

          Rate INDEX REGEX
INDEX 340657/s    --  -65%
REGEX 973582/s  186%    --

          Rate INDEX REGEX
INDEX  40348/s    --  -74%
REGEX 155495/s  285%    --

         Rate INDEX REGEX
INDEX  3530/s    --  -77%
REGEX 15077/s  327%    --