[profsnuggles]

Lets take your tar example. The -z and -x options are flags, they specify binary on/off options. You can specify all the flags separately on the command invocation like so:

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

However typing -flag -flag2 -flag3 is too many keystrokes so an a convenience you can combine all the flags in one call -xzf. The -f isn't a flag though it takes an argument which in this case is the filename foo.tar.gz. The argument is required and comes directly after the flag. Which is why the f has to come last because that argument has to come right after. Order doesn't matter for the x and z because they don't take arguments they are just flags. It makes sense if you add in another flag like -C which also takes an option you would end up with:

  $ tar -xzfC foo.tar.gz directory_to_change_to

Which argument goes to which flag? Maybe the first flag gets the first argument? Then your argument order changes if you type in the flags backwards.

I don't know about your z flag, GNU tar doesn't need it. The x flag is needed because tar can do things other than extract like list the contents of the archive with the -t flag, or create a new archive with -c.

Finally why is the f command required? My first assumption was that maybe because you need to specify the output file when you are creating an archive. I took a look in the manpage and the reason is a lot more interesting.

  Use archive file or device ARCHIVE.  If this option is not given, tar will
  first examine the environment variable `TAPE'. If it is set, its value will
  be used as the archive name. Otherwise, tar will assume the compiled-in
  default.

I knew that tar's name comes from the phrase tape archive but I hadn't put two and two together. Of course you need to specify if you are writing the archive to a file because tar was created to back up data to tape! If you think about it tar is actually doing the "right thing". Considering why it was written tar has a sane default, write the data to the tape drive.

Maybe you already understand all this and I'm reading too much into your simple example. It feels to me though that when people have issues with something like the unix command line its because they just wanted to get something done and memorized an incantation to do it. There isn't anything wrong with that of course but a tool like tar is SO much more powerful than just decompressing files. Once you start to dig into it though there is an internal consistency and logic to it though.

[loup-vaillant]

> Maybe you already understand all this

Yes I do. Every single item. I just feel for the hapless student that is required to send a compressed archive of his work to the teacher, and is using tar for the first time.

There's only one little exception: I didn't know GNU tar doesn't require the '-z' flag (which by the way means 'this is a gzip archive') when extracting tar.gz archive. Anyway, I bet my hat that the '-z' is required if you compress something and output the result to the standard output: there will be no '.gz' hint to help the tool magically understand you want it compressed. If you omit it, tar will likely not compress anything.

The '-f' option is the most aggravating. Nobody uses tapes any more. Tar was doing the right thing, but no longer. -f should be dropped, or rendered optional, or replaced by '-o' for consistency with compilers… As it is, it's just ugly.

> It feels to me though that when people have issues with something like the unix command line its because they just wanted to get something done and memorized an incantation to do it. There isn't anything wrong with that of course […]

Actually there is. The users want to do something (usually a very common case such as compressing or decompressing an archive), then they have to memorise an arcane incantation. Yes, tar can do much more. Yes, the command line is powerful and flexible and more. This is Good. (Seriously, I miss my command line whenever I have to touch Windows.) On the other hand, some common cases are just not well handled, and it is full of idiosyncrasies that have nothing to do with the aforementioned benefits.

When the user wants to decompress files, it should not be more complicated than 'decompress archive.tar.gz'. Though thanks to an uncle comment, I now know of the 'unp' tool, which works just like that: 'unp archive.tar.gz', and you're done. (And the man page is refreshingly short.)