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say for do {                    # <-- mixed paradigms --------
   my %seen;                    # <-- reinventing the wheel  |
...
   map  { ( split m{;} )[ 1 ] } # too much logic, but that's nitpickin
+g
   <$inFH>;
   };'

use List::Util qw(uniqstr);
say join "\n", 
...
   map  { $_->[0] }
   map  { [ split m{;} ] }
   <$inFH>;