Linux 版 (精华区)
发信人: netiscpu (说不如做), 信区: Linux
标 题: [B] Red Hat Linux Unleashed (14)
发信站: 紫 丁 香 (Sat Jul 25 03:10:19 1998), 转信
Shell Programming
_________________________________________________________________
o Using the write Command
# A Description of the write Command
# A Sample write Session
# write Etiquette
o The talk Communication Tool
# A Sample talk Session
# talk Etiquette
o Electronic Mail
# Mailboxes and Agents
# Understanding the Mail Message
# Types of Mail User Agents
@ Using elm
@ Using Pine
@ Using mailx (Berkeley Mail)
o Using news
# nn
# tin
@ Command-Line Options
o Using FTP
# Anonymous FTP
@ ftp Commands
o telnet
o Summary
_________________________________________________________________
14
Using Communication Tools Under Linux
The communication tools discussed in this chapter include the
following:
* write: For one-way communication with other users
* mesg: For controlling message reception from other users
* talk: For an interactive connection with other users
* e-mail: For sending and receiving messages
* telnet: For logging into remote sites
* ftp: For remote file transfers
* news: For reading news via nn and tin
This chapter discusses all of these communications tools in detail and
gives you the basics of how to use them in Linux. With practice, you
will soon begin to use these tools effectively.
Using the write Command
The write command is a communication tool that enables a user to
interact directly with other users. If you want to ask your friend a
simple question or ask her out to lunch, and you know that she is
logged in, write is the tool to use. Unlike e-mail, which is discussed
later, write pastes your message directly on the recipient's terminal.
The recipient does not have to take any steps to receive it.
To use the write command, your terminal and that of the other user
should have write permission. Having these permissions enables you to
write messages on each other's terminals. To look at the terminal
settings, you need to know which terminal you are on. To find your
terminal number, use the tty command as shown here:
mpsi:~$ tty
/dev/tty2
mpsi:~$ ls -al /dev/tty2
crw—w—w- 1 calvin users 4, 2 Jan 15 05:49 /dev/tty2
The preceding code sample shows that I am on /dev/tty2. Your output
may be different, depending on which terminal you happen to be on. The
output of the ls command shows that others have write permission
available on your terminal. You can confirm this by using the mesg
command as shown here:
mpsi:~$
mpsi:~$ mesg
Is y
The outcome of the mesg command shows that the terminal enables
messages to be written to it. You can toggle the terminal settings on
and off with the following command:
mpsi:~$ mesg n
mpsi:~$ mesg
Is n
The preceding segment turned the mesg off. Now you can't be disturbed
by any other user. (You may miss out on lunch dates, though.)
A Description of the write Command
The write command enables you to write an actual message on the other
terminal online. You have to issue the write command with the login ID
of the user with whom you want to communicate. The write command
informs the user at the other end that there is a message from another
user. write pastes that message onto the other user's terminal if
their terminal's write permissions are set. Even if they are in the
middle of an edit session, write overwrites whatever is on the screen.
The edit session contents are not corrupted; you can restore the
original screen on most editors with Ctrl-L. write is mostly used for
one-way communication, but you can have an actual conversation as
well.
______________________________________________________________
NOTE: For the write command to work, mesg has to be turned on, so
turn it back on.
______________________________________________________________
A Sample write Session
Because you want your friend to be able to write to your tty as well,
always begin by checking the status of the mesg command:
mpsi:~$
mpsi:~$ mesg
Is y
Let's see whether your friend Calvin is logged in. You can do this by
using the who command and piping it to the grep program to search for
Calvin, because you don't want the entire list of users to scroll down
your terminal.
mpsi:~$ who | grep calvin
calvin tty2 Jan 15 15:26
______________________________________________________________
NOTE: Don't forget to type /dev before the terminal name. Look at
what happens when you don't type the /dev string:
mpsi:~$ ls -l tty2
ls: tty2: No such file or directory
Oops! All the ttys are in /dev, so add /dev to tty2.
______________________________________________________________
Now let's see whether he wants to be disturbed:
mpsi:~$ ls -al /dev/tty2
crw—w—w- 1 calvin users 4, 2 Jan 15 15:28 /dev/tty2
mpsi:~$
This excerpt shows you that Calvin is indeed logged in. Now let's see
whether he is interested in communicating with a write session:
mpsi:~$ write calvin
Calvin sees the following on his screen:
mpsi:~$
Message from laurel@mpsi on tty1 at 15:36 ...
Now you have to wait for Calvin's response to the request. He responds
by typing the following on his terminal if he is interested in
communicating with you:
mpsi:~$ write laurel
How are you?
Lunch tomorrow?
The following string appears on your terminal:
Message from calvin@mpsi on tty2 at 15:36 ...
How are you?
Lunch tomorrow?
You can answer Calvin by initiating another write session from your
end and typing your message. You have to press Enter at the end of
each line for it to be displayed at the other terminal. To simplify
communications, you can type over at the logical end of your sentence.
Calvin should do likewise.
write Etiquette
If you are waiting for the other party to respond to your write
request, it is polite to let him reply while you wait. Only after he
has accepted your invitation should the conversation begin. Also, let
the called party have the first chance to reply by typing hello or any
other salutation. Avoid typing until the other party stops or signals
you to begin with an end-of-message word, such as over. Remember, only
one person can speak at a time on this channel.
The talk Communication Tool
The write tool was nice for communicating one at a time. However,
Linux enables you to type simultaneously with the talk tool.
talk is an interactive communication tool that enables you to have an
actual conversation in real-time mode with another user. You can
actually see the conversation being typed as the other user is typing
it. For talk to work, the other user has to be logged in, just as in
write.
talk can be very annoying and disturbing if someone wants to be pesky.
If you don't want to be disturbed, just turn talk off by entering mesg
n at the prompt.
A Sample talk Session
You can talk to somebody by typing talk followed by the user's login
ID. To see if the user is logged in, you can use the who command just
like you did for write. Let's try to talk to Calvin:
$ talk calvin
The computer responds with
[Waiting for your party to respond]
The user on the other end sees the following message even if he is in
the middle of an edit session. The system beeps and displays the
following message on the terminal:
Message from Talk_Daemon@mpsi at 13:08 ...
talk: connection requested by laurel@hobbes.com.
talk: respond with: talk laurel@hobbes.com
To respond to this, type the command shown in the respond with message
shown here. If your friend does not respond, the talk daemon
persistently bothers him with the preceding message every 30 seconds.
At your terminal, you see the following messages:
[Ringing your party again]
[Ringing your party again]
[Ringing your party again]
[Ringing your party again]
Occasionally you will see the following message:
[Your party is refusing messages]
What happened? Your friend at the other end does not want to talk or
be disturbed. After several of your interruptions, he has decided to
turn his mesg off. That is why you got the message that your party is
refusing messages.
Now let's look at a nicer scenario, when someone wants to talk to you.
He has to respond with the following command:
talk laurel.
Then your terminal displays the following screen:
[Connection Established]
—————————————&
#151;————————————&#
151;————————————
51;
The screen is divided horizontally with a dotted line, and you can
type your message on the top half of the screen. This appears verbatim
on the other terminal at the bottom half of the screen. You can type
your messages, and the other user can type his, simultaneously.
The connection can be closed by entering Ctrl-C. The following line
appears on the screen:
[Connection closing.Exiting]
You should now be back at your shell's command prompt.
talk Etiquette
The same etiquette applies to talk as in write. Always use lowercase
letters, because CAPS LOCK conversations are considered loud and rude.
Always finish your sentence by typing over. If you initiated the talk
session, wait for the other party to respond with the hello first. To
prevent both of you from typing at the same time, always read your
message, wait for the over, type your own message, and then terminate
it with over.
Electronic Mail
Electronic mail has taken the world by storm. E-mail, short for
electronic mail, is a method of sending a message from a user on one
computer to one or several recipients on another computer. E-mail
provides fast and efficient transportation of data and documents. This
mode of communication also eliminates the need to play telephone tag
or to wait for a convenient or appropriate time to call someone. For
someone with Internet access, e-mail provides the means to communicate
with friends around the world.
Mailboxes and Agents
E-mail is stored in a file called the system mail in the mailbox.
System mail has the same name as that of the user. For example, a user
named Calvin will have a mailbox under Linux in
/var/spool/mail/calvin.
E-mail originates in the form of a file on your computer created by a
Mail User Agent (MUA). E-mail is then submitted to a mail router such
as sendmail, after which it is handed over to a Mail Transporter Agent
(MTA). E-mail is then appended to a mailbox. The MTA delivers it to
the final delivery agent by traversing one or more hosts.
The MUA is used to read and send mail. The MUA is the user interface
for the mail system. Mail can be composed by using simple MUAs such as
mail or mailx, or sophisticated mail user agents such as elm or pine.
Understanding the Mail Message
A mail message includes two parts: a mail header and the text body.
The mail header is generated by the mail program automatically. A
typical header in a mail message looks like this:
Date: Fri, 6 Jan 1995 13:27:00 -0600
From: "Calvin N. Hobbes" <calvin@hobbes.com>
To: laurel@hady.com
Subject: Format for a mail header
Hi, just checking the different parts in a mail message
Date specifies the date and time the message is sent.
From specifies both the sender's name in quotes and the address, which
includes the login ID and the address of their machine, hobbes.com.
To is the recipient's mail address.
Subject is a one-line description of the mail message.
The mail header is followed by the body of the mail message. Here you
type the message as text. The mail message is terminated by typing a
period (.) as the first character on the last line. The mail handler
responds with EOT, for End Of Text. This is the standard procedure for
Berkeley mail; other mail handlers have their own way of ending
message text entry.
Types of Mail User Agents
There are several types of mail user agents, some of which are listed
here. A variety of different programs can be used for reading the
mail. The two most common programs are mail and Mail (also called
mailx). Because of the similarity of their names, Mail is also called
capmail or Berkeley Mail. Berkeley Mail is far superior to mail
because it is much easier to use.
This section covers the following types of mail user agents:
* elm
* Pine
* mailx (Berkeley Mail)
Using elm
elm stands for electronic mail and provides a full-screen interface
mail program with a good help feature. elm is a pleasure to use when
compared with Berkeley Mail because of its simplicity of use and
functionality.
Start the elm system by typing elm at the command prompt:
$ elm
The screen is cleared, and the code shown in the following screen is
displayed.
$ elm
Mailbox is '/var/spool/mail/calvin' with 5 messages [ELM 2.4 PL25]
N 1 Jan 12 Laurel N. Hardy (15) using el
N 2 Jan 12 Laurel N. Hardy (15) 2nd elm message
N 3 Jan 12 Laurel N. Hardy (16) Using elm
N 4 Jan 11 Laurel N. Hardy (11) Re: Format for a mail header
N 5 Jan 11 Laurel N. Hardy (11) message # 1
You can use any of the following commands by pressing the first character;
d)elete or u)ndelete mail, m)ail a message, r)eply or f)orward mail, q)uit
To read a message, press <return>. j = move down, k = move up, ? = help
<M1>
Command:
The top line on the screen is the mailbox and the number of messages
it has in it. You may also see elm's version number. This is followed
by a list of all the messages in the mailbox, the date the messages
were sent, the sender's name, and the subject of the message.
The current message is indicated by an arrow or inverse video.
One nice feature of elm is that it displays the sender's name instead
of the login ID as Berkeley Mail does.
The bottom part of the screen lists the options available. At this
point, you can reply to the message, delete or undelete a message, or
forward the mail by entering the appropriate command. You can go up
and down the message list by using k and j, just as in the vi editor.
Some of the actions available in elm are listed in Table 14.1.
Table 14.1. elm actions.
Command elm 2.4 Action
Enter, Spacebar Displays current message.
| Pipes current message or tagged messages to a system command.
! Shell escape.
? This screen of information.
= Sets current message to first message.
* Sets current message to last message.
<NUMBER>, Enter Sets current message to <NUMBER>.
/ Searches From/Subjects for pattern.
// Searches entire message texts for pattern.
> Saves current message or tagged messages to a folder.
< Scans current message for calendar entries.
C Copies current message or tagged messages.
c Changes to another folder.
d Deletes current message.
Ctrl-D Deletes messages with a specified pattern.
e Edits current folder.
f Forwards current message.
g Groups (all recipients') reply to current message.
h Headers displayed with message.
J Increments current message by one.
j, <DOWN> Advances to next undeleted message.
K Decrements current message by one.
k, <UP> Advances to previous undeleted message.
l Limits messages by specified criteria.
Ctrl-L Redraws screen.
m Mails a message.
[lb] Next message, displaying current, then increment.
p Prints current message or tagged messages.
q Quits, maybe prompting for deleting, storing, and keeping messages.
Let's try to send mail using elm.
To send mail, press m on the main screen. The header screen appears.
elm prompts you to enter the name(s) of the recipient(s) of the mail.
Enter calvin and root as recipients. Calvin is the primary recipient,
and a copy of this message is sent to root as well.
elm then prompts for a subject. After entering the subject heading,
elm puts you in the vi editor to enter the body of the mail message.
After you are finished typing, use the vi command :wq to save and quit
the vi editor. You can now send the message by pressing s.
You can also forward mail to others on the system with the f command
or reply to a message with the r command.
To quit elm, type q at the main screen.
If elm is available on your system, try to use it. elm is very
convenient and simple and can greatly improve your electronic mail
interaction.
Using Pine
Pine, a trademark of the University of Washington, stands for Program
for Internet News and E-mail. Pine offers the capability to send local
and remote messages using a simple user interface as well as the
capability to send documents and graphics.
You invoke Pine by entering pine on the command line. The screen shown
here should appear.
$ pine
PINE 3.91 MAIN MENU Folder: INBOX 1 Message
? HELP - Get help using Pine
C COMPOSE MESSAGE - Compose and send a message
I FOLDER INDEX - View messages in current folder
L FOLDER LIST - Select a folder to view
A ADDRESS BOOK - Update address book
S SETUP - Configure or update Pine
Q QUIT - Exit the Pine program
Copyright 1989-1994. PINE is a trademark of the University of Washington.
[Folder "INBOX" opened with 1 message]
? Help P PrevCmd R RelNotes
O OTHER CMDS L [ListFldrs] N NextCmd K KBLock
Pine is very easy to use, because it provides a full-screen interface
with the up and down cursor controls. Simply select the item you want
by using the arrow keys and press Enter at the selected line.
Let's send a message using Pine. Take the cursor to the Compose
Message line and press Enter. The screen shown here appears.
PINE 3.91 COMPOSE MESSAGE Folder: INBOX 1 Message
To : "Laurel N. Hardy" <laurel@hobbes.com>
Cc :
Attchmnt:
Subject : using pine
—— Message Text ——
Hi, I can do everything on one screen
.
Send message? [y] :
^G Get Help ^X Send ^R Rich Hdr ^Y PrvPg/Top ^K Cut Line ^O Postpone
^C Cancel ^D Del Char ^J Attach ^V NxtPg/End ^U UnDel Line ^T To AddrBk
Pine takes you line-by-line through the mail header and the mail
message. Press Ctrl-X to end the message as well as send it to the
recipient. Just walk through all the options to get a feel for this
mail system.
The last two lines on the screen tell you what commands are available
for the current situation. Usually there are more commands than can be
shown on two lines, so use the O key to see what other commands are
available. The O is optional; you don't have to be able to see a
command before you use it.
Pine creates a default configuration file, .pinerc, in your home
directory. You can edit this file to select various options. Pine also
creates a mail subdirectory for your saved-message folders. Type ?
from the Main Menu for more help.
Using mailx (Berkeley Mail)
This section is about mailx, another common mail program for Linux.
This section covers the basics of mailx. mailx has many options and
features, most of which are listed in its man pages. Discussing all
these features would require a book in itself.
Let's see how to receive and send mail using mailx.
Receiving Mail
Suppose someone has sent you a mail message. How would you know about
it? The Mail system deals with this by displaying a message when you
log in. A sample login session is shown in the following screen.
Welcome to Linux 1.2.13.
mpsi login: laurel
Last login: Fri Jan 6 13:28:06 on tty1
Linux 1.2.13.
You have new mail.
To read the mail message, invoke the Mail handler by typing mail at
the prompt. You will see the output shown in the following screen.
mpsi:~$ mail
Mail version 5.5-kw 5/30/95. Type ? for help.
"/var/spool/mail/calvin": 1 message 1 new
>N 1 laurel@hobbes.com Fri Jan 6 13:38 12/374 "just checking"
& 1
Message 1:
From laurel@hobbes.com Fri Jan 6 13:38:06 1995
Date: Fri, 6 Jan 1995 13:38:06 -0600
From: "Laurel N. Hardy" <laurel@hobbes.com>
To: calvin@hobbes.com
Subject: just checking
the body of the message
bye
& exit
You have mail in /var/spool/mail/calvin
In this example, the user Calvin has received a mail message from
another user, Laurel. This message is the first message in the message
queue and is declared as new, which means it has not been read yet.
The message queue has an >N, indicating that it is a new message,
followed by a message number (1), the sender's login ID
(laurel@hobbes.com), the day of the week, the date and time the
message was sent, and the subject of the message.
The ampersand (&) is the mail system prompt. You can now read the
message by typing the message number at this prompt.
& 1
Message 1:
From laurel@hobbes.com Fri Jan 6 13:38:06 1995
Date: Fri, 6 Jan 1995 13:38:06 -0600
From: "Laurel N. Hardy" <laurel@hobbes.com>
To: calvin@hobbes.com
Subject: just checking
the body of the message
bye
&
Mail Options
All the available options in the Mail system can be listed by typing a
? after the &. The listed options are shown in Listing 14.1.
Listing 14.1. Mail options.
& ?
Mail Commands
t <message list> type messages
n goto and type next message
e <message list> edit messages
f <message list> give head lines of messages
d <message list> delete messages
s <message list> file append messages to file
u <message list> undelete messages
R <message list> reply to message senders
r <message list> reply to message senders and all recipients
pre <message list> make messages go back to /usr/spool/mail
m <user list> mail to specific users
q quit, saving unresolved messages in mbox
x quit, do not remove system mailbox
h print out active message headers
! shell escape
cd [directory] chdir to directory or home if none given
A <message list> consists of integers, ranges of same, or user names separated
by spaces. If omitted, Mail uses the last message typed.
A <user list> consists of user names or aliases separated by spaces.
Aliases are defined in .mailrc in your home directory.
&
Replying to a Message
Suppose you have three mail messages from different users and you want
to reply to the one sent by Jeremy. Just invoke mail as before, as
shown in Listing 14.2.
Listing 14.2. Three received messages.
mpsi:~$ mail
Mail version 5.5-kw 5/30/95. Type ? for help.
"/var/spool/mail/laurel": 3 messages 3 unread
>U 1 calvin@hobbes.com Fri Jan 6 13:27 12/429 "Format for a mail hea"
U 2 jeremy@hobbes.com Sat Jan 7 15:25 72/23291 " Please reply soon"
U 3 calvin@hobbes.com Wed Jan 11 12:29 12/373 "message # 3"
The U in front of the second message specifies that the message is
still unread. You can read the message by typing the message number.
& 2
Message 2:
From jeremy@hobbes.com Sat Jan 7 15:25:00 1995
Date: Sat, 7 Jan 1995 15:25:00 -0600
From: "friend22" <jeremy@hobbes.com>
To: laurel@hobbes.com
Subject: Please reply soon
What's up?
You can reply to the message by typing r.
& r
To: jeremy@hobbes.com
Subject: Re: Please reply soon
Replying to your mail message # 2
I am too busy to reply to you now. Go away.
.
EOT
The Mail daemon automatically sets up the header in the reply mode, so
all you have to do is type the text.
Sending and Forwarding Mail
Sending and forwarding mail can be done with the s and f commands,
respectively. The procedures for creating the header and text of the
message are similar to that of replying to a message.
The ~/signature file is appended to every mail message you send. You
should place text in here that you want to send with every message.
Some examples are your phone number or an alternative e-mail address
(your recipient might not be able to reply to certain hosts). Mail
etiquette requires that you keep you signature files short—four
lines or less. Most recipients do not like to see pages of information
about you in every mail message.
Using news
Using news is perhaps the best way of getting into what is probably
the world's best online forum: the Usenet news service. There are
literally thousands of giant bulletin boards for you to select topics
from and post messages to. The number of subjects available can be
quite overwhelming at times, since there are more than 13,000
newsgroup topics to choose from. (A newsgroup is one of the bulletin
boards.) Newsgroups offer the best example of free speech and a forum
for discussing just about any topic imaginable.
Topics range from the serious to the absurd. In the serious category
you can talk about computer communications (comp.dcom.telecom),
astronomy (sci.astro), and so forth. In the absurd corner you have
alt.tasteless, alt.barney.dinosaur.die.die.die, and
alt.fan.oj-simpson.drive.faster.
Usenet was started at Duke University in 1979 by two students, Tom
Truscott and Jim Ellis, as an experiment to connect two computers
between Duke and the University of North Carolina. From these two news
sites in 1980, the number of news sites has grown to hundreds of
thousands of sites in the 1990s, with millions of subscribers
worldwide.
There are several news readers for Linux. I will cover two: nn and
tin.
nn
The nn news reader stands for Net News. When you use nn, you decide
which of the many news groups you are interested in. You unsubscribe
those that do not interest you any more. nn lets you read all articles
in each of the groups you subscribe to, using a menu-based article
selection prior to reading the articles in the newsgroup.
When you enter a newsgroup in nn, you are presented with a screen that
lists the most recent unread articles. Each item on this list contains
at least the sender and subject. You are now in selection mode. You
can select using the A through Z and 0 through 9 keys. When you select
an article, it is displayed in a highlight color. If you press the
spacebar, you go into read mode.
In read mode, nn presents you with each article. Press the spacebar to
get to the next page of each article. If you are at the end of an
article, the spacebar takes you to the next article.
When you have read all the selected articles in the current group,
pressing the spacebar takes you to the next group.
Here are some of the other commands in nn:
* ? or help gives a one-page overview of the commands available in
the current mode. This is perhaps the most used command for
beginners. The best way to learn about nn is by using this
command.
* Ctrl-L or Ctrl-R redraws the screen.
* Ctrl-P shows the previous message.
* ! is the shell escape command. You are prompted for a command if
you do not type one after the !.
* Q quits nn.
* V prints release and version information (for debug).
* :command executes the command by name. This is used to invoke any
of nn's commands, including those that cannot be bound to a key.
The nn man pages provide about 600 lines of very detailed information
about all the options and commands available to you. You do not have
to use all of them—just use as many as necessary to customize
your own environment.
tin
tin is a screen-oriented Net News reader. It can read news locally
(/var/spool/news) or remotely (rtin or tin -r option) via an NNTP
(Network News Transport Protocol) server. tin is based on the tass
newsreader, which was developed by Rich Skrenta in March 1991. tass
was itself heavily influenced by NOTES, which was developed at the
University of Illinois by Ray Essick and Rob Kolstad in 1982. The most
relevant author to date is Iain Lea (iain.lea@erlm.siemens.de). Check
the long list of contributors in the man pages.
______________________________________________________________
NOTE: Use the h (help) command to view a list of the commands
available at any level.
______________________________________________________________
On startup, tin shows a list of the newsgroups found in $HOME/.newsrc.
An arrow (->) or highlighted bar points to the first newsgroup. Move
to a group by using the terminal arrow keys or j and k. Use Page Up
and Page Down or Ctrl-U and Ctrl-D to page up and down. Select a
newsgroup to read from by pressing Enter.
The Tab key advances to the next newsgroup that has unread articles
and enters it.
To start and run tin, export NNTPSERVER to the address of your remote
news server. Use the command
$ export NNTPSERVER=news.your.provider.com
Then run tin with the -r option to connect to this remote server.
A sample tin session is shown in Listing 14.3. It shows two newsgroups
that I have subscribed to: alt.humor and tx.jobs.
When you select a message to read from and press either the right
arrow or Enter key, you are shown the message itself, as shown in
Listing 14.4.
Listing 14.3. A sample tin session.
Group Selection (news.neosoft.com 2) h=help
1 571 alt.humor
u 2 398 tx.jobs
=set current to n, TAB=next unread, /=search pattern, c)atchup,
g)oto, j=line down, k=line up, h)elp, m)ove, q)uit, r=toggle all/unread,
s)ubscribe, S)ub pattern, u)nsubscribe, U)nsub pattern, y)ank in/out
Group tx.jobs ('q' to quit)...
Listing 14.4. Another sample tin session.
tx.jobs (368T 401A 0K 0H R) h=help
171 + US-TX-Dallas MicroFocus Cobol Contract Mark Allen
172 + CA-CLARIS HR, WINDOWS DEVELOPMENT POSITIONS A CLARIS HR
173 + CA-CLARIS HR, DIRECTOR OF WORLDWIDE PRODUCT D CLARIS HR
174 + CA-CLARIS HR, INTERNATIONAL WINDOWS ENGINEER CLARIS HR
175 + CA, CLARIS CORP - TELECOMMUNICATIONS ANALYST CLARIS HR
176 + CA- CLARIS HR, SYBASE PROGRAMMER/ANALYST AT C CLARIS HR
177 + CA-CLARIS HR, DOCUMENTATION CONTROL SPECIALIST CLARIS HR
178 + CA-CLARIS, SUPERVISOR, DIRECT ACCOUNT SERVICE CLARIS HR
179 + CA-DEVELOPERS & TEST ENGINEERS - JAPANESE PRO CLARIS HR
180 + CA-CLARIS HR, DATABASE INTERNALS ENGINEER POS CLARIS HR
181 + CA, CLARIS CORPORATION - PRICING ANALYST CLARIS HR
182 + WA-CLARIS HR, MAC & WINDOWS DEV'RS/ INTERFACE CLARIS HR
183 + USA-TX-DALLAS - Informix 4GL/ESQL imi
184 + USA-TX-DALLAS - SONET Telephany Engineers imi
185 + USA-TX-DALLAS - PowerBuilder imi
186 + USA-TX-DALLAS - Oracle DBAs imi
187 + USA-TX-DALLAS - CICS, Cobol, JCL, VSAM (ALC + imi
=set current to n, TAB=next unread, /=search pattern, ^K)ill/select,
a)uthor search, c)atchup, j=line down, k=line up, K=mark read, l)ist thread,
|=pipe, m)ail, o=print, q)uit, r=toggle all/unread, s)ave, t)ag, w=post
In Listing 14.4, you see a list of subject headers and their index
numbers. The + sign indicates that you have not read this message. For
example, the SONET job for Dallas, Texas, has an index of 184 and is
unread. To read this message, use the arrow keys to move to it, and
then press Enter.
Command-Line Options
tin has several command-line options, some of which are listed in
Table 14.2.
Table 14.2. tin's command-line options.
Option Description
-c Creates or updates index files for every group in $HOME/.newsrc or
every file specified by the -f option and marks all articles as read.
-f file Uses the specified file of subscribed newsgroups instead of
$HOME/.newsrc.
-h A help listing of all command-line options.
-m dir The mailbox directory to use. The default is $HOME/Mail.
-n Loads only groups from the active file that are also subscribed to
in the user's .newsrc. This enables a noticeable speedup when
connecting via a slow line.
-p program Prints program with options.
-q quick Starts without checking for new newsgroups.
-r read News specified in the environment variable NNTPSERVER or
contained in the file /etc/nntpserver.
-R read News saved by -S option (not yet implemented remotely from the
default NNTP server).
-s dir Saves articles to a directory. The default is $HOME/News.
-v Verbose mode for the -c, -M, -S, -u, and -Z options.
To add a new group, type ggroupname. For example, gmisc.invest adds
the newsgroup misc.invest.
tin offers an emacs-style editing facility for entering messages. The
command strings include a history of commands to enable reuse of
previous commands. The man pages for tin list all the commands
available to you for editing, deleting, and removing messages.
tin uses the following important environment variables:
NNTPSERVER The default NNTP server to remotely read news from. This
variable needs to be set only if the -r command-line option is
specified and the file /etc/nntpserver does not exist.
VISUAL This variable overrides the default editor that is used in all
editing operations within tin.
tin can pretty much be navigated by using the four arrow keys. The
left arrow key goes up a level; the right arrow key goes down a level;
the up arrow key goes up a line or page; and the down arrow key goes
down a line or page. Most prompts within tin can be aborted by
pressing Esc.
Using FTP
File transfer protocol (FTP) is a method of transferring files from
one computer to another. FTP provides the capability of transferring
files to and from a remote network site as well as means for sharing
public files. In this section you go through a sample FTP session and
follow the steps for finding and getting software from a remote site.
ftp is the user interface to the ARPANET standard FTP. The ftp service
is the interface to the file transfer protocol. It lets a user connect
to another site and send and receive files.
In this section you will try to get a file from the address
tsx-11.mit.edu by logging in as anonymous. This anonymous use of FTP
is very convenient and provides access to innumerable servers,
providing a wealth of information. Publicly accessible FTP servers are
called anonymous FTP servers.
Anonymous FTP
Anonymous FTP enables users to access remote sites without having an
authorized user ID and password. Generally the login ID is anonymous
and the password is guest. Most current systems require your e-mail
address as the password instead of guest.
______________________________________________________________
NOTE: FTP stands for File Transfer Protocol; ftp is the program you
run on Linux.
______________________________________________________________
The client host with which ftp is to communicate may be specified on
the command line. If this is done, ftp immediately attempts to
establish a connection to an FTP server on that host. Otherwise, ftp
enters its command interpreter and awaits instructions from the user.
When ftp is awaiting commands from the user, the prompt ftp> is
provided to the user. Enter ftp at the prompt, along with the site
address:
$ ftp hostname
A hostname can be either a hostname or an Internet address. For
example, you can use the following Internet address:
mpsi$ ftp tsx-11.mit.edu
If your system connects to the MIT server, the text shown in Listing
14.5 appears.
Listing 14.5. An ftp session.
220 tsx-11 FTP server (Version wu-2.4(3) Mon Jun 5 16:40:22 EDT 1995) ready.
Name (tsx-11.mit.edu:uzma): anonymous
331 Guest login ok, send your complete e-mail address as password.
Password:
230-Welcome, archive user! This is an experimental FTP server. If have any
230-unusual problems, please report them via e-mail to ftp-bugs@tsx-11.mit.edu.
230-If you do have problems, please try using a dash (-) as the first character
230-of your password — this will turn off the continuation messages that m
ay
230-be confusing your ftp client.
230-
230-The Linux archives are in /pub/linux/
230-
230-In most places, 'get <directory>.tar' will retrieve a tar file containing
230-that directory. 'get <file>.gz' gets a gzipped version of a files, and
230-'get <file>.Z' gets a compressed version of the file. 'get <dir>.tar.gz'
230-is possible, but not recommended. 'get <dir>.zip' will get a zip archive
230-with *NO* compression of the directory <dir>.
230-
230-If you find something on TSX-11 which doesn't work, or which you
230-believe is obselete, please send mail to ftp-linux@TSX-11.MIT.EDU.
230-INCLUDE THE FULL PATHNAME OF THE FILE AND WHY YOU THINK IT IS OBSOLETE.
230-
230- - Ted and Michael
230-
230 Guest login ok, access restrictions apply.
Remote system type is UNIX.
Using binary mode to transfer files.
ftp>
The first line confirms that the connection is established. Line 220
indicates that the FTP server is ready. The system then prompts for a
name, which is anonymous in this case, and a password. The password is
not echoed, so any typing mistakes you make are not apparent. You are
then connected to the remote FTP server, which awaits your commands.
ftp Commands
The ftp service enables the user to execute several commands. Some of
the local commands are listed in Table 14.3.
Table 14.3. Some ftp commands.
Command Description
[account [passwd]] Supplies a supplemental password required by a
remote system for access to resources once a login has been
successfully completed. If no argument is included, the user is
prompted for an account password in a non-echoing input mode.
ascii Sets the file transfer type to network ASCII. This is the
default type.
bell Sounds a bell after each file transfer.
binary Sets the file transfer type to binary mode.
bye Terminates the FTP session with the remote server and then exits.
cd remote-directory Changes the working directory on the remote
machine to the remote directory.
cdup Goes to the parent of the current remote machine's working
directory.
chmod mode file-name Changes the permission modes of the file.
close Terminates the FTP session with the remote server.
delete remote-file Deletes the remote file on the remote machine.
dir [remote-directory] Prints a listing of the remote directory to the
terminal.
disconnect Same as close.
get remote-file Retrieves the remote file and stores it on the local
machine. [local-file]
If the local filename is not specified, it is given the same name it
has on the remote machine.
hash While a file is being transferred, the hash sign (#) is printed
for each data block transferred.
help [command] Prints an informative message about the meaning of the
command. If no argument is given, ftp prints a list of the known
commands.
lcd [directory] Changes the working directory on the local machine. If
no directory is specified, the user's home directory is used.
ls [remote-directory] Lists the contents of the remote directory.
mdelete [remote-files] Deletes the remote files on the remote machine.
mdir remote-files Like dir, except multiple remote files may be
specified.
mget remote-files Expands the remote files on the remote machine and
does a getfiles based on regular expressions. For example, mget f*.tar
will get all the files starting with the letter f.
open host [port] Establishes a connection to the specified host FTP
server on the optional port number.
put local-file Stores a local file on the remote machine.
pwd Prints the name of the current working directory on the remote
machine.
quit Same as bye.
remotehelp [command-name] Requests help from the remote FTP server. If
a command name is specified, it is supplied to the server as well.
reset Resets the communications connection.
rmdir directory-name Deletes a directory on the remote machine.
size file-name Returns the size of the file on the remote machine.
status Shows the current status of ftp.
verbose Displays all responses to the user.
? [command] Same as help.
Some of the options that may be specified at the command line are
listed as follows:
-v The verbose option. Gives a report on the transfer statistics and
forces ftp to show all responses from the remote server.
-n Restrains ftp from attempting auto-login upon initial connection.
In auto-login, ftp checks for the user's account on the remote
machine.
-I Turns off interactive prompting during multiple file transfers.
-d Enables debugging.
Some ftp commands share the same name as Linux commands but perform a
different function. For example, the ls command in ftp behaves like
the ls-al command in Linux. To illustrate how this works, let's look
at the directory listing command on a remote server:
______________________________________________________________
NOTE: On some systems, ls at the ftp prompt will behave like the
ls-F command.
______________________________________________________________
ftp>
ftp> ls
200 PORT command successful.
150 Opening ASCII mode data connection for /bin/ls.
total 6
drwxrwxr-x 2 root ftp-linu 512 Feb 8 1995 bin
drwxrwxr-x 2 root wheel 512 Nov 5 1994 dev
drwxrwxr-x 3 root wheel 512 Nov 9 17:22 etc
lrwxr-xr-x 1 tytso wheel 1 Nov 5 02:17 ftp -> .
drwxrwx-wx 4 tytso ftp-linu 512 Dec 8 07:44 incoming
drwxrwxr-x 9 tytso ftp 512 Dec 1 22:35 pub
226 Transfer complete.
ftp>
As you can see, you did not have to type -al. You get the long listing
from the ls command.
To abort a file transfer, use the terminal interrupt key (usually
Ctrl-C). Sending transfers are immediately halted. Receiving transfers
are halted by sending an ftp ABOR command to the remote server and
discarding any further data received.
The ftp specification specifies many parameters that may affect a file
transfer. The type may be ascii, image (binary), or ebcdic.
telnet
The telnet command is used to communicate with another host using the
TELNET protocol. If telnet is invoked without the host argument, it
enters command mode, indicated by its prompt, telnet>. Normally you
would use
$ telnet hostname [port]
where hostname is the host you want to connect to and port indicates a
port number (an application's address). If a number is not specified,
the default telnet port is used.
telnet can log you in either one of two modes: character-by-character
or line-by-line. In character-by-character mode, most text typed is
immediately sent to the remote host for processing. In line-by-line
mode, all text is echoed locally, and only completed lines are sent to
the remote host.
While connected to a remote host, you can enter the telnet command
mode by typing the telnet escape character, Ctrl-]. When in command
mode, the normal terminal editing conventions are available.
The following commands are available under the command mode:
close Closes a telnet session and returns to command mode.
open host Opens a connection to the named host. If no port number
[[-l] user][-port]is specified, telnet attempts to use the default
port. The [-l] option may be used to specify the user name.
quit Closes any open telnet session and exits telnet. An end-of-file
(in command mode) will also close a session and exit.
Check the man pages for a list of long, detailed options for telnet.
Let's use telnet to do an Archie session. An Archie server is helpful
for searching for files by giving a keyword in a title. See Listing
14.6.
Listing 14.6. Logging in via telnet.
$ telnet archie.internic.net
.
.
.
SunOS UNIX 4.1 (ds) (ttypa)
login: archie
********************************************************************
Welcome to the InterNIC Directory and Database Server.
*******************************************************************************
*
# Bunyip Information Systems, 1993, 1994
# Terminal type set to 'vt100 24 80'
# 'erase' character is '^?'.
# 'search' (type string) has the value 'sub'.
archie>
The archie> prompt is asking you for input. Let's look at some of the
help information available for Archie. Type help at the archie>
prompt. See Listing 14.7 for a sample output.
Listing 14.7. Help for Archie.
archie >help
These are the commands you can use in help:
. go up one level in the hierarchy
? display a list of valid subtopics at the current level
<newline>
done, ^D, ^C quit from help entirely
<string> help on a topic or subtopic
Eg.
"help show"
will give you the help screen for the "show" command
"help set search"
Will give you the help information for the "search" variable.
The command "manpage" will give you a complete copy of the archie manual page.
~
~
(END)
Now let's try to find a file on HylaFAX. Use the command find, as
shown in Listing 14.8. The sub string indicates that you are searching
for the word in the entire filename and are not looking for an exact
match.
Listing 14.8. Finding by keyword.
archie> find hylafax
# Search type: sub.
# Your queue position: 1
# Estimated time for completion: 00:33
working... \
The results of the match are shown in Listing 14.9. You can scroll up
and down with the k and j keys. The spacebar scrolls one page. The
Enter key scrolls down one line at a time. You can stop the listing
with the q key.
Listing 14.9. The output of the Archie command.
Host freebsd.cdrom.com (192.153.46.2)
Last updated 11:06 30 Jan 1994
Location: /.1/FreeBSD/FreeBSD-current/ports
DIRECTORY drwxr-xr-x 1024 bytes 01:17 4 Dec 1993 flexfax
Location: /.1/FreeBSD/FreeBSD-current/ports/hylafax/man
FILE -rw-rw-r— 15254 bytes 15:45 31 Aug 1993 flexfax.1
Location: /.1/FreeBSD/FreeBSD-current/ports/hylafax/dist
FILE -rw-rw-r— 17 bytes 15:40 31 Aug 1993 flexfax.alpha
FILE -rw-rw-r— 2671 bytes 15:40 31 Aug 1993 flexfax.spec
Location: /.1/FreeBSD/FreeBSD-current/ports/hylafax/port/386bsd
FILE -rw-rw-r— 2828 bytes 15:45 31 Aug 1993 Makefile.flexfax
Location: /.1/FreeBSD/FreeBSD-current/ports/hylafax/port/4.4bsd
FILE -rw-rw-r— 2839 bytes 15:45 31 Aug 1993 Makefile.flexfax
Location: /.1/FreeBSD/FreeBSD-current/ports/hylafax/port/bsdi
FILE -rw-rw-r— 2837 bytes 15:46 31 Aug 1993 Makefile.flexfax
db/tmp/AAAa26919
After you are finished with Archie, you can log off the server. This
closes the telnet connection. You can get your HylaFAX files via FTP
from these sites.
Summary
The communication tools discussed in this chapter were write, talk,
mesg, and mail. You also learned about nn and tin for reading news
from the Internet. For getting files from remote sites, you learned
how to use FTP. With the telnet session, you also learned a bit about
Archie, an archival search utility.
As you can see, Linux offers a wide variety of communication tools.
This chapter has merely introduced you to these tools. You have to
work with each tool to learn its intricacies. Happy communicating.
--
Enjoy Linux!
-----It's FREE!-----
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