In unix, how can I pipe the output of who into the groups command?

Question

I'm trying to do something like this:

Say there are 4 users logged into a UNIX machine, a, b, c, and d.

Now, to get the groups these guys belong to, I have to type out :

groups a b c d.

What I am wondering, is if there is a way to do something like who | groups where I can pipe the users currently logged-in to the groups command, which would then print out all the users given along with their group information. However, this does not seem to work as intended - rather, the above command just gives the group the first user belongs to.

Answer 1

In bash, zsh, and others:

groups $(who | cut -d' ' -f 1)

Answer 2

Though I have not checked this one:

who -q | xargs -o groups

But you should be able to use xargs for this

• http://en.wikipedia.org/wiki/Xargs

Answer 3

groups $(who -q)|head -n -1

Answer 4

who | while read -r user line; do echo "$user $line" -- `groups $user`; done

This will output the "who" command with the groups on the side