The write command lets you send a message directly to someone else who is logged on to the system. To determine who is logged on, use the who command. The who command displays information about who is logged on in this form:

BUBBA    ttyp0002                  Feb 8 09:49

where BUBBA is a login name, ttyp0002 is the terminal, and Feb 8 09:49 is the login time.

The typical format of the write command is:

write user_name

However, if a user is logged in more than once, you can specify terminal (in the ttyp form that who returns) rather than user_name.