This gem is called repackage. It allows the user to repackage a given archive, such as from foobar-1.0.tar.gz towards foobar-1.0.tar.xz format. If the target archive (the input that is given to the main class of this gem) can not be found then the current behaviour is to first try a glob-operation, such as via Dir[], before giving up, since as of version 1.0.2 of this gem.