Homework & Coursework Questions

The output of the first command gets funneled into the input of the second command; that's just how pipes work in shell.

If you do sort | who that's trying to put the output from sort into the input of who, which is a command that doesn't even read anything, so it doesn't make much sense.

You got it.

Code:

$ who | sort

You probably already know the best way to learn is to log on and play around on the computer. You're right if only two people are on (you and the admin) that you can't really test "who" very well. In that case, you can create a little test file, and do some experiments, such as:

Code:

$ echo Joe > test.txt
$ echo Bill >> test.txt
$ echo Suzy >> test.txt
$ echo Alice >> test.txt
$ cat test.txt
Joe
Bill
Suzy
Alice
$ sort test.txt
Alice
Bill
Joe
Suzy
$ cat test.txt | sort
Alice
Bill
Joe
Suzy
$ sort < test.txt
Alice
Bill
Joe
Suzy

I used "echo" to make the test.txt file. If you know how to use a Unix editor, of course use the editor instead.

With the test file, you can try out different sort options, as you are already doing with -r option.

Yes, that is exactly right! "who" produces the output, the "raw materials". The output from "who" enters the pipe. On the other side of the pipe, "sort" reads its input. The output from "sort" is what you finally see.

"who" does not expect any input, so it would not make sense to put "who" on the right-hand side of the pipe. "sort" HAS to have input, or have a file specified for it to operate upon. In the examples above, I showed three simple ways sort can get input (sort file, | sort, and sort < file).

You should open a new thread.