Using write to send a message or a file
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.