A number of archive formats such as DAR, AR, tar come under the GNU GPL license.
If I understand correctly I only need to license my software as GPL if I use any APIs provided by libraries which manipulate the archive (e.g., libdar).
So if I write my own software to manipulate the archive(eg. a way to read it) I can release it under a license of my choice?
e.g., libarchive is released under the more lenient BSD license but has capabilities of manipulating GPL licensed archive format types.