declare a hash (e.g. "my %lines."
open the first input file
while reading the first input one line at a time
   use the line as a hash key and assign "1" as the hash value
close the file

open output.file1 to hold "matching lines"
open output.file2 to hold "distinct lines"

open the second input file
while reading the second input one line at a time
   if the current line exists as a hash key and the hash value is "1"
     print this line to the "matching lines" file
     increment the hash value
   otherwise
     print this line to the "distinct lines" file (maybe include the file name)

having read all input, now loop over all the keys of the hash
   if the hash value assigned to this key is still "1"
     print this hash key to the "distinct lines" file (maybe include the file name)