$str = '123456789';
cmpthese -1, {
 a=>q[ my ($a,$b) = $str =~  m/(23)[^8]+(8)/g; ],
 b=>q[ my ($a,$b) = $str =~  m/(23)[^8]+(8)/; ],
 c=>q[ my ($a) = $str =~  m/(23)/g ],
 d=>q[ my ($a) = $str =~  m/(23)/; ],
};;
      Rate    b    a    d    c
b 388799/s   -- -14% -37% -52%
a 449698/s  16%   -- -27% -44%
d 612922/s  58%  36%   -- -24%
c 806251/s 107%  79%  32%   --