Well something is wrong with if ($File2Parts{$PartNumber}) That statement checks for "truthfullness" of the value of that hash key's value.

Add: use Data::Dumper; at the top of the code. Then before the F1 loop, print Dumper \%$File2Parts; That will show you what is actually in the hash table. Data::Dumper is a "core module" meaning that it is already "pre-installed" in Perl. Look for spaces or other characters that would cause the hash key from file2 to not compare with the PartNumber from file1.

Of course use some abbreviated files for testing otherwise you will get a lot of output that is not helpful!