gzip compression

gzip compresses a single file, gunzip expands it. tar does not compress on its own, so the pair is joined into .tar.gz.

gzip -k file        # compress, -k keeps the original
gunzip file.gz      # expand
gzip -t a.tar.gz    # check it is valid gzip
gzip -l a.tar.gz    # sizes and compression ratio

gzip -t checks integrity against the checksum inside the archive. The ratio depends on the data: text compresses well, already-compressed data (images, video) barely at all.

Used in

You need this in the lesson Archives: tar and gzip.