UUCP Chat Script Field (System Administration Guide: Resource Management and Network Services)

System Administration Guide: Resource Management and Network Services

UUCP Chat Script Field

This field (also called the Login field) contains a string of characters that is called a chat-script. The chat-script contains the characters the local and remote machines must pass to each other in their initial conversation. Chat-scripts have the following format:

expect send [expect send] ....

expect represents the string that the local host expects to receive from the remote host to initiate conversation. send is the string the local host sends after it receives the expect string from the remote host. A chat-script can have more than one expect-send sequence.

A basic chat-script might contain the following:

Login prompt that the local host expects to receive from the remote machine
Login name that the local host sends to the remote machine in order to log in
Password prompt that the local host expects to receive from the remote machine
Password that the local host sends to the remote machine

The expect field can be composed of subfields of the following form:

expect[-send-expect]...

send is sent if the prior expect is not successfully read, and the -expect that follows the send is the next expected string.

For example, with strings login--login, the UUCP on the local host expects login. If UUCP receives login from the remote machine, it goes to the next field. If it does not receive login, it sends a carriage return, then looks for login again. If the local computer initially does not expect any characters, use the characters "" (NULL string) in the expect field. All send fields are sent with a carriage return appended unless the send string is terminated with a \c.

Here is an example of a Systems file entry that uses an expect-send string:

System-Name  Time  Type  Speed  Phone     Chat Script
sonora Any ACUEC 9600 2223333 "" \r \r ogin:-BREAK-ogin: Puucpx ssword: xyzzy

This example tells UUCP on the local host to send two carriage returns and wait for ogin: (for Login:). If ogin: is not received, send a BREAK. When you do receive ogin: send the login name Puucpx. When you receive ssword: (for Password:), send the password xyzzy.

The following table lists some useful escape characters.

Table 40-2 Escape Characters Used in Systems File Chat Script


Escape Character	Meaning
`\b`	Sends or expects a backspace character.
`\c`	If at the end of a string, suppresses the carriage return that is normally sent. Ignored otherwise.
`\d`	Delays 1-3 seconds before sending more characters.
`\E`	Starts echo checking. From this point on, whenever a character is transmitted, UUCP waits for the character to be received before continuing its checks.
`\e`	Echoes check-off.
`\H`	Ignores one hangup. Use this option for dialback modems.
`\K`	Sends a BREAK character.
`\M`	Turns on `CLOCAL` flag.
`\m`	Turns off `CLOCAL` flag.
`\n`	Sends or expects a newline character.
`\N`	Sends a NULL character (ASCII NUL).
`\p`	Pauses for approximately 1/4 to 1/2 second.
`\r`	Sends or expects a carriage return.
`\s`	Sends or expects a space character.
`\t`	Sends or expects a tab character.
`EOT`	Sends an EOT, followed by newline twice.
`BREAK`	Sends a break character.
`\ddd`	Sends or expects the character that is represented by the octal digits (`ddd`).

Enabling Dialback Through the Chat Script

Some companies set up dial-in servers to handle calls from remote computers. For example, your company might have a dial-in server with a dialback modem that employees can call from their home computers. After the dial-in server identifies the remote machine, it disconnects the link to the remote machine and then calls back the remote machine. The communications link is then reestablished.

You can facilitate dialback by using the \H option in the Systems file chat-script at the place where dialback should occur. Include the \H as part of an expect string at the place where the dial-in server is expected to hang up.

For example, suppose the chat-script that calls a dial-in server contains the following string:

INITIATED\Hogin:

The UUCP dialing facility on the local machine expects to receive the characters INITIATED from the dial-in server. After the INITIATED characters have been matched, the dialing facility flushes any subsequent characters it receives until the dial-in server hangs up. The local dialing facility then waits until it receives the next part of the expect string, the characters ogin:, from the dial-in server. When it receives the ogin:, the dialing facility then continues through the chat-script.

You need not to have a string of characters directly preceding or following the \H, as shown in the previous sample string.