$s = 'x'x3000 . 'reg exp' . 'x'x3000; 
cmpthese -1, { 
    REGEX => q[ $x = $s =~ /reg exp/;], 
    INDEX => q[ $x = index $s, 'reg exp';] 
};;
          Rate INDEX REGEX
INDEX  40470/s    --  -74%
REGEX 156392/s  286%    --