I'm wondering if there is a way to delete the already decompressed portion of a file as it is being decompressed. I've got an external backup of the compressed file so I'm not worried about loosing data. The file is a bz2. I'm looking to do this because I've only got 50 GB available on the drive and the compressed file is 33 GB. If I can't delete portions of the file while extracting then there won't be enough space for the decompressed file.
There are other things I could do to get around this but I am interested to know if what I mentioned above is possible.
In general, it is not possible to delete the initial portion of a file - you can only truncate a trailing portion of it.
Newer Linux kernels, however, support punching holes into files for specific filesystems, using the fallocate() system call. There is a corresponding utility that can be used for the same purpose, although you need a relatively recent version (2.21 or later) of the util-linux package for hole punching support to be included in that utility.
Keep in mind that hole punching is still relatively new and kernel bugs still pop-up - you might be better off just cleaning up your filesystem to free some space.