You need to log in manually to know what to write for the PPP script.

To know what strings to expect, it is a good idea to go through the login process manually, at least once. Below is an actual screen dump of a session I had with Internet Direct. In particular, 416-233-2999. Other numbers to Internet Direct may vary in what is output and in how you are prompted. Certainly, other ISPs will be different from this one. minicom is usually the modem dialer of choice if you decide to log in manually.

A Manual Login (using minicom) - Responses are in red:

AT &F
OK

atdt*70,4162332999

CONNECT 14400/V42BIS
Welcome to Internet Direct!

If you already have a User-ID on this
system, type it in and press RETURN.
Otherwise type "new" at the login: prompt.

login: my_username
Password: XXXXXXXXX

Please wait...

Type SLIP, CSLIP, PPP
or press [ENTER] to continue:  PPP
Your IP address is 207.136.100.16.
Server address is 207.136.82.56.
PPP Ready.
          ~y}#.!}!6}
}8}!}$}%U}"}&} } } } }%}&}$=pc}'}"}(}".Q~~y}#.!}!7} }8}!}$

Let's look at the strings.

AT &F

This is a standard string sent to the modem to tell it to reset itself to the factory-set defaults. We need not concern ourselves wth this string,as pppd does the settings for us.


OK

This is what the modem responds with. It is the first thing our chat script sees. So we should make a note of it. This tells us that all systems are "go" and we can dial.


atdt*70,4162332999

Upon seeing the "OK", I enter the number to dial, prefixed by "atdt", which specifies tone dialing, as opposed to pulse dialing. The "*70," tells the phone operator to disable call waiting, which can wreak major havoc with dialing in. This should be standard practice for all calls you make by modem, not just the PPP calls. You hear the modem dial, you hear the ringing, then the squelch, then you see:


CONNECT 14400/V42BIS

Your modem is now telling you that you have connected at the desired speed. My modem is 14.4kbps; your mileage may vary. This is only informational, but we should still make a note of it. It is important since it tells us that the ISP's modem has answered before the timeout, and a connection has been made. Then we see:


Welcome to Internet Direct!


If you already have a User-ID on this
system, type it in and press RETURN.
Otherwise type "new" at the login: prompt.

login: my_username

Obviously, when your chat script sees the word "login", that is your next cue to respond with a username. We ought to make note of this also. But wait ... If I use "login:" as the expect string, you can see it appears in two places above. It is likely that my chat script will send my username in response to the first "login:", and by the time it sees the second, the username will have already been received and ignored by the host. This was great when you dialed in manually, since you do not want the host to buffer every stray keystroke you make until the actual prompt. But now it is an impediment, since keystrokes are not an issue with chat scripts. But this will not impede us for long. We can also specify expect strings for the chat script to ignore.
 

Password: XXXXXXXXX

Once this impediment is overcome, the rest is easy. The word "Password:" appears once in this session, so you can respond straight away with a password.


Please wait...


Type SLIP, CSLIP, PPP
or press [ENTER] to continue:  PPP

On the prompt "or press [ENTER] to continue:", which is also unique, send the response "PPP" to the host.

Writing the Chat script:

So, now we have a list of 6 expect strings:

1. OK
2. CONNECT
3. Otherwise type "new" at the login: prompt.
4. login:
5. Password:
6. or press [ENTER] to continue:

Additional Notes:

#!/bin/bash

The chat script that is posted on the previous page used #!/bin/sh (the Bourne Shell), which is really the same shell in LINUX, since they are symbolically linked. You can use nearly any shell you like. This just tells the kernel to invoke a subshell to run the script commands.

Now we have to give it the command to execute:

exec chat -v                                         \

We need the -v option in "chat" so that detailed output can be sent to /var/log/messages for debugging. Note the "\" on the far right side of the line. That is a continuation mark, telling the shell that there is more to be added to the command after the carriage return.

You must set a timeout value for the modem to respond. 3 seconds is forever for something that is sitting on your motherboard. Also, indent this to show that it is part of the "chat" command.

TIMEOUT 3                                       \
ABORT         '\nBUSY\r'                        \
ABORT         '\nNO ANSWER\r'                   \
ABORT         '\nRINGING\r\n\r\nRINGING\r'      \
''            \rAT                              \

We also need to tell the modem what to do if the chat receives an "ABORT". If we don't get anything from the modem, test it  (using "AT"). If things are fine, the modem should respond with an "OK"

'OK-+++\c-OK'  ATH0                             \

Depending on the make of the modem, there are a variety of responses possible, usually involving the string "OK", but sometimes with other characters intervening. This was from the original PPP script that came with the downloaded ppp software. My modem gives a simple "OK", but in case there are some weird modems out there, it has to be compatible. Before dialing, we must make absolutely sure the modem is hung up, so send "ATH0" to hang it up if it is not.

TIMEOUT       45                               \

Now we shall change the timeout value of the modem for dialing in. Anything from 30 to 60 seconds is reasonable. Any more would test your patience too much, but your mileage may vary on that too. The modem will hang up if it takes more than 45 seconds for the ISP to answer with this setting.

OK            ATDT$TELEPHONE                   \

We should expect an OK. Now we will send the number to dial. The exported shell variable "TELEPHONE" is set in the file /etc/scripts/ppp-on

CONNECT       ''                               \

Shows that we're connected. If the chat script didn't see this by the timeout of 45 seconds, it would have hung up. If the chat does see this before the timeout, then it just sends an empty string and continues.

Other--prompt. '\r'                            \

This string contains the beginning and end of the bogus "login:" string. Notice that the word "login" and all other words between the beginning and end is left out, and replaced with dashes to signify that there are intervening characters. We are sending a string that contains a carriage return ("\r").

login:        p$ACCOUNT                        \

Once we get the real login prompt, we send the username. For some reason, on my modem the first character is ignored. So I now give it a character followed by my username, as set in the script ppp-on.

Password:      $PASSWORD                        \

This is followed by the password, which does not suffer from the same problem. On your host, you may notice that the "login" and "Password" may be quite different. Both may be in lowercase, upper case, initial uppercase, with or without the colon, and so on. You have to check for these things in minicom, so that your chat script will be appropriate. If your login and Password prompts differ by an initial upper or initial lowercase letter, then you can place two dashes before the words, leaving out the "L" and "P".

or--continue:  ppp

And this is where we are asked to enter the "ppp" string.