How to decompress only a portion of a file

You can pass the -S option to use a suffix other than .gz.

gunzip -S .compressed file.compressed

If you want the uncompressed file to have some other name, run

gzip -dc <compressed-file >uncompressed-file
gunzip <compressed-file >uncompressed-file

(these commands are equivalent).

Normally unzipping restores the name and date of the original file (when it was compressed); this doesn't happen with -c.

If you want the compressed file and the uncompressed file to have the same name, you can't do it directly, you need to either rename the compressed file or rename the uncompressed file. In particular, gzip removes and recreates its target file, so if you need to modify the file in place because you don't have write permission in the directory, you need to use -c or redirection.

cp somefile /tmp
gunzip </tmp/somefile >|somefile

Note that gunzip <somefile >somefile will not work, because the gunzip process would see a file truncated to 0 bytes when it starts reading. If you could invoke the truncation, then gunzip would feed back on its own output; either way, this one can't be done in place.

The command you're showing in your first line (tar -cvfz example2.tgz example1) doesn't work and it should not output any file example2.tgz. Didn't you get an error? Perhaps the file example2.tgz existed already? Check if you have a file called z in that folder - that's where the tgz has been saved to, because:

The -f parameter specifies the file which must follow immediately afterwards: -f <file>

Try

tar cvzf exam.tgz example1