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The who Command

The first program is the who command. By itself, it generates a list of the users who are currently logged in. Although I’m writing this on a single-user system, we’ll pretend that several people are logged in:

$ who
-| arnold   console Jan 22 19:57
-| miriam   ttyp0   Jan 23 14:19(:0.0)
-| bill     ttyp1   Jan 21 09:32(:0.0)
-| arnold   ttyp2   Jan 23 20:48(:0.0)

Here, the ‘$’ is the usual shell prompt, at which I typed ‘who’. There are three people logged in, and I am logged in twice. On traditional Unix systems, user names are never more than eight characters long. This little bit of trivia will be useful later. The output of who is nice, but the data is not all that exciting.