Costello:  
Abbott, how do I see who is logged into the unix server. 

Abbott:  
who

Costello:  
Yes, who is on the server, what command do I use?

Abbott: 
No, what shows the revision of a binary.

Costello:
I don't know what shows the revision a binary.
I want to see who is on the system.

Abbott: 
who

Costello:
yes, who

Abbott: 
correct

Costello:
I don't think you understand.  I want the command to see who is on the system.

Abbott: 
Have you tried finger.

Costello:
I don't need to give the finger to any user, 
I just want to know which command I use.

Abbott: 
which command will tell you the path to the command

Costello:
I don't know which command to tell me the path.
I just want to find who!

Abbott: 
Just use find / -name who.
It should list who as /usr/bin/who.

Costello:
So /usr/bin/who will let me see all the users on a system, yes?

Abbott: 
No, yes no longer exists, try ckyorn.

Costello:
You aren't making sense.

Abbott: 
You cannot make sense unless that rule is defined your Makefile.

Costello:
What rule?

Abbott: 
That will give you the version of the rule binary.

Costello:
But what is the command to list users on a system.

Abbott: 
who

Costello:
You that's who, I've been talking to you and no one else!

Abbott: 
talk only works for valid users.
You don't need to shout.

Costello:
Ok, who lists who is on the system,
what lists the version of a binary,
find lists all the matches of a file,
and which tells me the path to an executable.

Abbott:
That's right!

Costello:
I am going to exit now.

Abbott:
You most certainly may, but exist only takes numeric arg, not strings.