So, a friend of mine sent me a file with extension .run.gz saying that its a pretty good game. I decided to give it a try and started to extract it, but wait! I got the error saying that it is not a gzip archive. Something was definitely wrong. I was totally confused, thinking "What the hell!!" . The mystery was finally revealed when I ran file command. It stated that the file is a "POSIX shell script text executable".