V10/man/man1/write.1

.TH WRITE 1
.CT 1 comm_term comm_users
.SH NAME
write, mesg \- write to other users, allow or forbid messages
.SH SYNOPSIS
.B write
.I person ...
.PP
.B mesg
[
.B n
]
[
.B y
]
.SH DESCRIPTION
.I Write
copies lines from your terminal to terminals of other
.I persons
designated either by login name or
(to circumvent occasional ambiguities) by terminal name
as given by
.IR who (1).
It announces to each
.I  person
your login name, your terminal,
and the other
.I persons.
To respond, each recipient should execute a corresponding
.I write
to the
.I  persons
he wants to talk to.
.PP
When you are writing to more than one person, your
messages are identified to the recipients.
Writing ceases upon end of file or interrupt,
and the message
.B EOF
is sent to the others.
.PP
.I Write
recognizes certain commands during a conversation:
.TP
.BI ! cmd
Execute a shell on the string
.I cmd
and then return to
.IR write .
.TP
.BI :a " person"
Add
.I person
to the list of people to whom you are talking,
and send an appropriate announcement to all parties.
They must do
.B :a
for themselves if they want to include the new person.
.TP
.BI :d " person"
Drop
.I person
from your list and make appropriate announcements.
.TP
.B :l
Print a list of people to whom you are talking.
.PP
The following protocol is suggested for using
.IR write .
When you invoke
.I write,
wait for the other user to
write back before starting to send.
Each party should end each message with a distinctive signal 
that the other may reply \- the customary convention is
.L (o)
for `over';
.B (oo)
for `over and out' is suggested when conversation
is about to be terminated.
.PP
.I Mesg
with argument
.B n
forbids messages via
.IR  write (1)
by revoking non-user
write permission on the user's terminal.
.I Mesg
with argument
.B y
reinstates permission.
All by itself,
.I mesg
reports the current state without changing it.
.PP
Certain commands, in particular
.I nroff
and
.IR  pr (1)
disallow
messages in order to prevent messy output.
.SH FILES
.TF /etc/utmp
.TP
.F /etc/utmp
to find user
.TP
.F /bin/sh
to execute 
.L !
.SH "SEE ALSO"
.IR who (1), 
.IR mail (1), 
.IR vismon (9.1)
.SH DIAGNOSTICS
.I Mesg
yields exit status 0 if messages are receivable, 1 if not,
2 on error.
.SH BUGS
.IR Mux (9.1)
generally prevents the receipt of
.I write
messages, but 
.IR vismon (9.1)
permits them.
.br
Messages ought to be identified when the recipient is receiving from
more than one writer, rather than when a writer is sending
to more than one recipient,
but that requires cooperating processes and isn't
worth the effort.