our $s = '123456789' x 100_000;
cmpthese -1, {
 a=>q[ my ($a,$b) = $s =~  m/(23)[^8]+(8)/g; ],
 b=>q[ my ($a,$b) = $s =~  m/(23)[^8]+(8)/; ],
 c=>q[ my ($a) = $s =~  m/(23)/g ],
 d=>q[ my ($a) = $s =~  m/(23)/; ],
};