grep { s/\d+/a/ } @dd;

##</code><code>##

@dd = map { s/\d+/a/r } @dd;

##</code><code>##

for (@dd) { s/\d+/a/; }

##</code><code>##

s/\d+/a/ for @dd;

##</code><code>##

$ perl -E'@dd = 0..9; s/\d+/a/ for @dd;                     say @dd;'
aaaaaaaaaa

$ perl -E'@dd = 0..9; s/\d+/a/ for grep { 1 } @dd;          say @dd;'
aaaaaaaaaa

$ perl -E'@dd = 0..9; s/\d+/a/ for do { @dd };              say @dd;'
aaaaaaaaaa

$ perl -E'@dd = 0..9; s/\d+/a/ for sub :lvalue { @dd }->(); say @dd;'
aaaaaaaaaa

$ perl -E'@dd = 0..9; s/\d+/a/ for sub { @dd }->();         say @dd;'
0123456789

$ perl -E'@dd = 0..9; s/\d+/a/ for map { $_ } @dd;          say @dd;'
0123456789

$ perl -E'@dd = 0..9; s/\d+/a/ for eval { @dd };            say @dd;'
0123456789