System info about a user. Try: finger root. An admin needs it all the time

finger user_name

#finger root
Login: root                             Name: root
Directory: /root                        Shell: /bin/bash
Last login Tue Nov 27 20:19 (IST) on tty1
No mail.
No Plan.

The command cmp is similar to diff:

# cmp file1 file2
file1 file2 differ: byte 10, line 1