Shell Programming and Scripting

Code:

who | cut -d ' ' -f1 > whoson
cut -d: -f1 /etc/passwd | grep -vf whoson

It can be done with standard commands.

#!/bin/ksh
# Who is logged in now?
who -u | awk '{print $1}' >/tmp/who_u.$$
# Who has an account?
logins | awk '{print $1}' > /tmp/logins.$$$

Code:

$ logins
-bash: logins: command not found

# Users who appear in "logins" but not in "who -u"
cat /tmp/logins.$$ /tmp/who_u.$$ | sort | uniq -u | pg

UUOC.

Sort will be slow on a large system, and it's not needed.

bash: pg: command not found

# Clean up temporary files
rm /tmp/logins.$$
rm /tmp/who_u.$$

You don't need two calls to rm:

Code:

rm /tmp/logins.$$ /tmp/who_u.$$

That is irrelevant. All solutions should use a POSIX shell and standard commands.

The logins command is not available on Mandriva, Red Hat, FreeBSD or NetBSD.

The pg command is on NetBSD, but not the others.

Neither command is part of the POSIX specification.

Why would you use non-standard commands when there are standard ones that do the job?

In a forum where people have many different systems, the only sensible thing is to post solutions that work for all of them.