[tedunangst]

You don't specify -f to tell it you're processing a file, you specify -f to tell it that the next argument is the filename. And it doesn't have to come last.

    tar -z -f foo.tar.gz -x

That's a perfectly valid tar command. Also, obviously you have to tell it that you're extracting the file. How else would it know that you don't want to create an archive?

[loup-vaillant]

You're the second commenter who believed I didn't know this stuff.

I know that, and more. But go and explain each and every flag to a student that just want to extract the first lesson of his first UNIX course. At this point, this is all magic and arbitrary.