On AIX 6.1 without GNU Tool installed I have a .tar.gz file.On Ubuntu I would use the very useful command :  tar xzf myfile.tar.gzbut in this case the z switch is not possible.I do remeber a long time ago a way to use gzip | tar but I really can't remember.  Can someone help me with that with a command that could work on almost every system even oldfashion unix ?
portable command to unzip and untar on non GNU and old unix
tar;aix;gzip;hp ux
Make gzip feed the uncompressed tar archive to tar:gunzip < myfile.tar.gz | tar xvf -(note that it's what GNU tar actually does internally, except that it will also report gunzip errors in its exit status).Use gzip -d if gunzip is not available. You might also have a zcat, but that one may only work with .Z files (compressed with compress instead of gzip).