use 5.012003;
use warnings;

my $str = "abacadabra";
my $rex = qr{(a\w)};

say "-- say";
say for ($str =~ m/$rex/g);

say "-- while";
while ($str =~ m/$rex/g) {
    say $1;
    }

->

-- say
ab
ac
ad
ab
-- while
ab
ac
ad
ab