use feature 'say';

$test = 'abc1234asf';

$test =~ /(?<one>\w{4})(?<two>\w{4})/;

#say 'one:', $+{one};            #works
#say 'two:', $+{two};

$test =~ s/(?<three>\w{4})(?<four>\w{4})/$+{four}$+{three}/;

say 'one:', $+{one};            #NOT works
say 'two:', $+{two};
say;
say 'three:', $+{three};
say 'four:', $+{four};
say;
say 'output:', $test;

OUTPUT:
-------

one:
two:

three:abc1
four:234a

output:234aabc1sf