Using use diagnostics; in addition to use warnings; will give you more information that is sometimes helpful in debugging your problem. It is also a good practice to use strict;.

Update: something unrelated to consider: you keep opening your OUT and HEAD filehandles within your first while loop, but you do not close them until you are out of the loop.

In reply to Re: Uninitialized value in concatenation by toolic
in thread Uninitialized value in concatenation by eiglesias

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