groups - (BSD) show group memberships
/usr/local/heirloom/usr/ucb/groups [user ...]
The groups command shows the groups to which you or the optionally
specified user belong. Each user belongs to a group specified in the password
file /etc/passwd and possibly to other groups as specified in the file
/etc/group. If you do not own a file but belong to the group which it
is owned by then you are granted group access to the file.
When a new file is created it is given the group of the containing
directory.