.MH "Subsystem Communication Services"
.#
.#
.bq
Communication utilities are becoming increasingly important
in today's computer systems.
The Subsystem, in keeping up with the times, offers as
its most important communication facilities a postal and
news service and a real-time communication system.
.eq
.#
.#
.SH "The Subsystem Postal Service"
.#
.#
In order to facilitate communication among users, the
Subsystem supports a postal service in the form of the 'mail' command.
'Mail' can be used in either of two ways:
.be
] [bf mail]
.ee
which looks to see if you have been sent any mail, prints
it on your terminal, and asks if you would like your mail
to be saved, or
.be
] [bf mail login_name]
.ee
which accepts input from standard input and sends it to the
mailbox of the user whose login name is "login_name".  Used in this
fashion, 'mail' reads until it sees an end-of-file. From the terminal,
this means until you type a control-c in column 1.
Your letter is postmarked
with the day, date and time of mailing and with your login name.
.pp
Whenever you enter the Subsystem (by typing 'swt') a check is made to see
if you have received any mail. If you have, you are told so.
When you receive your mail (by typing 'mail'),
you are asked if you want it to be saved.
If you reply "n", the mail you have just received will be discarded.
Otherwise, it is appended to the file "=mailfile=", which is located
in your profile directory.
(You can look at it
with 'cat', print it with 'pr', or do anything else you wish to it,
simply by giving its name to the proper command.
For example,
.be
] [bf cat =mailfile=]
.ee
would print all your saved mail on your terminal.)
[cc]mc |
.pp
If you have declared the shell variable "_mail_check",
(but not set it), the shell will check your mail file every
60 seconds, to see if it has increased in size.  If it has,
the shell will tell you, "You have new mail."  You may then
read your mail with the 'mail' program.
If you want it to check you mail more frequently, or less
frequently, you may set it to the number of seconds between
checks.  For instance:
.be
declare _mail_check = 300  # check mail every five minutes
.ee
By default, "_mail_check" will not be set for new users, so the shell
will only check your mail once, when the Subsystem is first
cranked up.
(See the
.ul
User's Guide for the Software Tools Subsystem Command Interpreter
for a more detailed discussion of the use of shell variables.
.pp
Due to the nature of the file system, setting "_mail_check" to less
than four will be no different than setting it to four.
At Georgia Tech, the mail directory is shared among several
machines, so, since the shell has to go across Primenet, you
should set "_mail_check" to a fairly large value, say 300,
for once every five minutes.
[cc]mc
.#
.#
.SH "The Subsystem News Service"
.#
.#
Whereas 'mail' is designed for person to person communication, the
Subsystem news service is intended for the publication of articles
that appeal to a more general interest. The news service is implemented
by three commands: 'subscribe', 'publish' and 'news'.
The use of the first two should be obvious.
.pp
If you wish to subscribe to the new service, simply type
.be
] [bf subscribe]
.ee
and then, whenever anyone publishes an article, a copy of it will be
delivered to your news box.
(You need subscribe to the news service only once; all
subscriptions are perpetual.)
Whenever you enter the Subsystem, as with
mail, a check is made to see if there is anything in your news box;
if there is, you are given a message to that effect.
.pp
Having gotten such a message, you may then read the news at your
convenience by typing
.be
] [bf news]
.ee
The news will be printed out on your terminal and then you will be asked
whether or not you want to save it. If you say "yes", it will be left in
your box and you may read it again at a later date; otherwise,
it is discarded. There are other ways to use
the 'news' command that are fully explained by 'help'.
.pp
Now suppose you have a hot story that you want to publish. All you
have to do is create a file (let's call it "article")
whose first line is the headline, followed by the text of the story.
Then you type
.be
] [bf publish article]
.ee
and your story will be delivered to all subscribers of the news service.
If you are a subscriber yourself,
you can check this with the 'news' command.
In addition, a copy is made in the news archives.
.pp
.ne 5
If you find that you have published the wrong article or if you
want to remove an outdated one, you can do a
.be
] [bf retract <article[bl]number>]
.ee
to remove the article, where <article[bl]number> is the sequence
number obtained from the news index ("news[bl]-i" will give you
such an index).  A retraction notice will be delivered to all
subscribers who have seen the article, and the article will simply
be removed from the news boxes of subscribers who have not yet seen it.
If you are only removing an outdated article, then using
.be
] [bf retract -q <article[bl]number>]
.ee
will quietly remove all traces of the article, leaving no
retraction notices behind to disturb those who have seen it.
.SH "Subsystem Real-Time Communications"
As if 'mail' and 'news' were not enough, the Subsystem offers
still another way to communicate with your fellow user, by means
of the 'to' command.  'To' allows you to communicate
with other logged-in users on a real-time basis;
messages that are sent to another user by the command
.be
] [bf to login_name <message>]
.ee
will be retrieved by the user whose login name is "login_name"
the next time his shell is ready
for a command.  Contrast this behavior to that of 'mail', where the
message must be retrieved by an action on the part of the addressee.
If <message> contains any of the shell's metacharacters,
it must be enclosed in quotes, as in:
.be
] [bf to allen "Where are you, and what are you doing?"]
.ee
.pp
If you want to send a multi-line message, 'to' will read your message
from standard input (just like most other Subsystem programs), so
that the only argument you would specify in this case would be the
login_name.  As always, a control-c in column 1
will generate an end-of-file to terminate your input.
.pp
Messages are only retrieved when the shell is ready for the next
command, so a user who is running a long program may not see
your messages until long after you have sent them.  If he logs out
before he sees your messages, they will sit there,
waiting to be retrieved until the next time he logs in.
[cc]mc |
.pp
To alleviate this somewhat, the Subsystem screen editor, 'se',
will notify you if there is a message waiting for you.
See the "om" command in the help on 'se' for details.
[cc]mc