It's still possible but you'll have to use something closer to what
sonofason wrote. For each match, you need to create a
($key, $value) pair so the list constructed by
map is more like
($key1, $value1, $key2, $value2, $key2, $value3) for the three values. That way, assigning to the hash will insert them as you want.
Now the code you can use to do that, can read for example:
@flat = map { /\w{3}_(\w)/ ? ($1, $_) : () } @inp;
It'll create a pair like
("A", "abc_A_bla") for a match, and an empty list for no match.
Assign to the hash, and you get:
%inp = map { /\w{3}_(\w)/ ? ($1, $_) : () } @inp;
