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PPP requires you to establish a modem connection to the remote machine before it can take over and handle the
communications. The chat program is the most commonly used of the utilities available to do this. The chat program
is popular because it uses a scripting style similar to that used by UUCP (see Chapter 27, "UUCP").
To use chat, you have to assemble a command line that looks almost the same as a UUCP /etc/Systems file entry. For
example, to call a remote machine with a Hayes-compatible modem (using the AT command set) at the number
555-1234, use the following command. It is all formatted as a chat script, UUCP style:
chat "" ATZ OK ATDT5551234 CONNECT "" ogin: ppp word: secret1
If you read the UUCP chapter, this code may look familiar. If not, all the entries are in a send-expect format, with
what you send to the remote specified after what you receive from it. The chat script always starts with an expect
string, which you must set to be empty because the modem won't talk to us without any signal to it. After the empty
string, send the ATZ (reset) command, wait for an OK back from the modem, and then send the dial command. Once
a CONNECT message is received back from the modem, the login script for the remote machine is executed. Send a
blank character, wait for the ogin: (login) prompt, send the login name ppp, wait for word: (password) prompt, and
then send your password. After the login is complete, chat terminates but leaves the line open.
If you want to see all the activity that goes on with the chat program, you can force all messages to the syslog daemon
for future study. The -v option forces the messages to syslog, so the command would be:
chat -v "" ATZ OK ATDT5551234 CONNECT "" ogin: ppp word: secret1
If the other end of the connection doesn't answer with a login script as soon as its modem answers, you may have to
force a Break command down the line to jog the remote end. This is done the same way as with UUCP:
chat -v "" ATZ OK ATDT5551234 CONNECT "" ogin:-BREAK-ogin: ppp word: secret1
Because any user doing a ps -ef command sees the entire command line (with its passwords), this type of chat entry
has a security problem. If you are the only user of your system, this isn't a concern, but to save yourself any problems,
you can embed the script portion of the command in a file and read the file in to chat. Then the script will not appear
on a ps output. To call a file for use with chat, use the -f option:
chat -f chat_file
The chat_file will contain the string:
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