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foo_1-a
foo_2-b
foo_3-b
...
bar_3-b
bar_4-a
bar_5-b

foo 4 foo_1-a foo_2-b foo_3-b foo_4-b
bar 5 bar_1-a bar_2-a bar_3-b bar_4-a bar_5_b

%hash_bar =()
bar_1-a => bar
bar_2-a => bar
...
foo_2-b => foo
foo_3-b => foo
foo_4-b => foo

open FH, "<file.txt";
while (<FH>)
    {
...
          $hash_$1($2)=$1;
          }
      }