[edflsafoiewq]

tar|gzip does not allow random access to files. You have to decompress the whole tarball (up to the file you want).

[jonjonsonjr]

Even worse, in the general case, you should really decompress the whole tarball up to the end because the traditional mechanism for efficiently overwriting a file in a tarball is to append another copy of it to the end. (This is similar to why you should only trust the central directory for zip files.)