The chat program defines a conversational exchange between the computer and the modem. Its primary purpose is to establish the connection between the Point-to-Point Protocol Daemon (pppd) and the remotes pppd process.
|-f <chat file>|
|Read the chat script from the chat file. The use of this option is mutually exclusive with the chat script parameters. The user must have read access to the file. Multiple lines are permitted in the file. Space or horizontal tab characters should be used to separate the strings.|
|Set the timeout for the expected string to be received. If the string is not received within the time limit then the reply string is not sent. An alternate reply may be sent or the script will fail if there is no alternate reply string. A failed script will cause the chat program to terminate with a non-zero error code.|
|-r <report file>|
|Set the file for output of the report strings. If you use the keyword REPORT, the resulting strings are written to this file. If this option is not used and you still use REPORT keywords, the stderr file is used for the report strings.|
|-e||Start with the echo option turned on. Echoing may also be turned on or off at specific points in the chat script by using the ECHO keyword. When echoing is enabled, all output from the modem is echoed to stderr.|
|-E||Enables environment variable substituion within chat scripts using the standard $xxx syntax.|
|-v||Request that the chat script be executed in a verbose mode. The chat program will then log the execution state of the chat script as well as all text received from the modem and the output strings sent to the modem. The default is to log through the SYSLOG; the logging method may be altered with the -S and -s flags.|
|-V||Request that the chat script be executed in a stderr verbose mode. The chat program will then log all text received from the modem and the output strings sent to the modem to the stderr device. This device is usually the local console at the station running the chat or pppd program.|
|-s||Use stderr. All log messages from -v and all error messages will be sent to stderr.|
|-S||Do not use the SYSLOG. By default, error messages are sent to the SYSLOG. The use of -S will prevent both log messages from -v and error messages from being sent to the SYSLOG.|
|-T <phone number>|
|Pass in an arbitary string, usually a phone number, that will be substituted for the \T substitution metacharacter in a send string.|
|-U <phone number 2>|
|Pass in a second string, usually a phone number, that will be substituted for the \U substitution metacharacter in a send string. This is useful when dialing an ISDN terminal adapter that requires two numbers.|
|script||If the script is not specified in a file with the -f option then the script is included as parameters to the chat program.|
The chat script defines the communications.
A script consists of one or more "expect-send" pairs of strings, separated by spaces, with an optional "subexpect-subsend" string pair, separated by a dash as in the following example:
|ogin:-BREAK-ogin: ppp ssword: hello2u2|
|This line indicates that the chat program should expect the string "ogin:". If it fails to receive a login prompt within the time interval allotted, it is to send a break sequence to the remote and then expect the string "ogin:". If the first "ogin:" is received then the break sequence is not generated.|
|Once it received the login prompt the chat program will send the string ppp and then expect the prompt "ssword:". When it receives the prompt for the password, it will send the password hello2u2.|
|A carriage return is normally sent following the reply string. It is not expected in the "expect" string unless it is specifically requested by using the \r character sequence.|
|The expect sequence should contain only what is needed to identify the string. Since it is normally stored on a disk file, it should not contain variable information. It is generally not acceptable to look for time strings, network identification strings, or other variable pieces of data as an expect string.|
|To help correct for characters which may be corrupted during the initial sequence, look for the string "ogin:" rather than "login:". It is possible that the leading "l" character may be received in error and you may never find the string even though it was sent by the system. For this reason, scripts look for "ogin:" rather than "login:" and "ssword:" rather than "password:".|
|A very simple script might look like this:|
|ogin: ppp ssword: hello2u2|
|In other words, expect ....ogin:, send ppp, expect ...ssword:, send hello2u2.|
|In actual practice, simple scripts are rare. At the vary least, you should include sub-expect sequences should the original string not be received. For example, consider the following script:|
|ogin:--ogin: ppp ssword: hello2u2|
# Now wait for the prompt and send logout string
These "abort" strings may be specified in the script using the ABORT sequence. It is written in the script as in the following example:
|ABORT BUSY ABORT NO CARRIER ATZ OK ATDT5551212 CONNECT|
SAY strings must be enclosed in single or double quotes. If carriage return and line feed are needed in the string to be output, you must explicitely add them to your string.
The SAY strings could be used to give progress messages in sections of the script where you want to have ECHO OFF but still let the user know what is happening. An example is:
SAY "Dialling your ISP...\n"
SAY "Waiting up to 2 minutes for connection ... "
SAY "Connected, now logging in ...0
$ SAY "Logged in OK ...0 etc ...
|This sequence will only present the SAY strings to the user and all the details of the script will remain hidden. For example, if the above script works, the user will see:|
Dialling your ISP...
Waiting up to 2 minutes for connection ... Connected, now logging in ...
Logged in OK ...
The report strings may be used to isolate the transmission rate of the modems connect string and return the value to the chat user. The analysis of the report string logic occurs in conjunction with the other string processing such as looking for the expect string. The use of the same string for a report and abort sequence is probably not very useful, however, it is possible.
The report strings to no change the completion code of the program.
These "report" strings may be specified in the script using the REPORT sequence. It is written in the script as in the following example:
|REPORT CONNECT ABORT BUSY ATDT5551212 CONNECT ogin: account|
ABORT NO CARRIER
Callback login: call_back_ID
ABORT "Bad Login"
Callback Password: Call_back_password
ABORT "NO CARRIER"
To change the timeout value for the next expect string, the following example may be used:
|ATZ OK ATDT5551212 CONNECT TIMEOUT 10 ogin:--ogin: TIMEOUT 5 assword: hello2u2|
The timeout, once changed, remains in effect until it is changed again.
|||Expects or sends a null string. If you send a null string then it will still send the return character. This sequence may either be a pair of apostrophe or quote characters.|
|\\b||represents a backspace character.|
|\\c||Suppresses the newline at the end of the reply string. This is the only method to send a string without a trailing return character. It must be at the end of the send string. For example, the sequence hello\c will simply send the characters h, e, l, l, o. (not valid in expect.)|
|\\d||Delay for one second. The program uses sleep(1) which will delay to a maximum of one second. (not valid in expect.)|
|\\K||Insert a BREAK (not valid in expect.)|
|\\n||Send a newline or linefeed character.|
|\\N||Send a null character. The same sequence may be represented by \0. (not valid in expect.)|
|\\p||Pause for a fraction of a second. The delay is 1/10th of a second. (not valid in expect.)|
|\\q||Suppress writing the string to the SYSLOG file. The string ?????? is written to the log in its place. (not valid in expect.)|
|\\r||Send or expect a carriage return.|
|\\s||Represents a space character in the string. This may be used when it is not desirable to quote the strings which contains spaces. The sequence HI TIM and HI\sTIM are the same.|
|\\t||Send or expect a tab character.|
|\\T||Send the phone number string as specified with the -T option (not valid in expect.)|
|\\U||Send the phone number 2 string as specified with the -U option (not valid in expect.)|
|\\\\||Send or expect a backslash character.|
|\\ddd||Collapse the octal digits (ddd) into a single ASCII character and send that character. (some characters are not valid in expect.)|
|^C||Substitute the sequence with the control character represented by C. For example, the character DC1 (17) is shown as ^Q. (some characters are not valid in expect.)|
|0||The normal termination of the program. This indicates that the script was executed without error to the normal conclusion.|
|1||One or more of the parameters are invalid or an expect string was too large for the internal buffers. This indicates that the program as not properly executed.|
|2||An error occurred during the execution of the program. This may be due to a read or write operation failing for some reason or chat receiving a signal such as SIGINT.|
|3||A timeout event occurred when there was an expect string without having a "-subsend" string. This may mean that you did not program the script correctly for the condition or that some unexpected event has occurred and the expected string could not be found.|
|4||The first string marked as an ABORT condition occurred.|
|5||The second string marked as an ABORT condition occurred.|
|6||The third string marked as an ABORT condition occurred.|
|7||The fourth string marked as an ABORT condition occurred.|
|...||The other termination codes are also strings marked as an ABORT condition.|