term% ls -F
term% cat index.txt
WRITE(1)                    General Commands Manual                   WRITE(1)

       write  -  write to another user

       write user [ ttyname ]

       Write  copies  lines  from your terminal to that of another user.  When
       first called, it sends the message

            Message from yourname yourttyname...

       The recipient of the message should write back at this point.  Communi‐
       cation  continues  until an end of file is read from the terminal or an
       interrupt is sent.  At that point write writes `EOT' on the other  ter‐
       minal and exits.

       If  you  want  to  write to a user who is logged in more than once, the
       ttyname argument may be used to indicate the appropriate terminal name.

       Permission to write may be denied or granted by use of  the  mesg  com‐
       mand.  At the outset writing is allowed.  Certain commands, in particu‐
       lar nroff and pr(1) disallow messages in order to prevent messy output.

       If the character `!' is found at the beginning of a line,  write  calls
       the shell to execute the rest of the line as a command.

       The  following  protocol  is  suggested for using write: when you first
       write to another user, wait for him to write back  before  starting  to
       send.  Each party should end each message with a distinctive signal—(o)
       for `over' is conventional—that the other may reply.   (oo)  for  `over
       and out' is suggested when conversation is about to be terminated.

       /etc/utmp to find user
       /bin/sh        to execute `!'

       mesg(1), who(1), mail(1)