CHAT(8) System Manager's Manual CHAT(8)
NAME
chat - Automated conversational script with a modem
SYNOPSIS
chat [ options ] script
DESCRIPTION
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 remote's pppd process.
OPTIONS
-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.
-t <timeout>
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 substitution 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 execu‐
tion 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 arbitrary 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.
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
This would be a better script than the simple one used earlier. This would look for the same login: prompt,
however, if one was not received, a single return sequence is sent and then it will look for login: again.
Should line noise obscure the first login prompt then sending the empty line will usually generate a login
prompt again.
COMMENTS
Comments can be embedded in the chat script. A comment is a line which starts with the # (hash) character in
column 1. Such comment lines are just ignored by the chat program. If a '#' character is to be expected as the
first character of the expect sequence, you should quote the expect string. If you want to wait for a prompt
that starts with a # (hash) character, you would have to write something like this:
# Now wait for the prompt and send logout string
'# ' logout
SENDING DATA FROM A FILE
If the string to send starts with an at sign (@), the rest of the string is taken to be the name of a file to
read to get the string to send. If the last character of the data read is a newline, it is removed. The file
can be a named pipe (or fifo) instead of a regular file. This provides a way for chat to communicate with
another program, for example, a program to prompt the user and receive a password typed in.
ABORT STRINGS
Many modems will report the status of the call as a string. These strings may be CONNECTED or NO CARRIER or
BUSY. It is often desirable to terminate the script should the modem fail to connect to the remote. The diffi‐
culty is that a script would not know exactly which modem string it may receive. On one attempt, it may
receive BUSY while the next time it may receive NO CARRIER.
CLR_ABORT STRINGS
This sequence allows for clearing previously set ABORT strings. ABORT strings are kept in an array of a pre-
determined size (at compilation time); CLR_ABORT will reclaim the space for cleared entries so that new
strings can use that space.
SAY STRINGS
The SAY directive allows the script to send strings to the user at the terminal via standard error. If chat
is being run by pppd, and pppd is running as a daemon (detached from its controlling terminal), standard error
will normally be redirected to the file /var/log/ppp/connect-errors.
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 explicitly 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:
ABORT BUSY
ECHO OFF
SAY "Dialling your ISP...\n"
'' ATDT5551212
TIMEOUT 120
SAY "Waiting up to 2 minutes for connection ... "
CONNECT ''
SAY "Connected, now logging in ...0
ogin: account
ssword: pass
$ 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 hid‐
den. 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 ...
REPORT STRINGS
A report string is similar to the ABORT string. The difference is that the strings, and all characters to the
next control character such as a carriage return, are written to the report file.
The report strings may be used to isolate the transmission rate of the modem's 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
This sequence will expect nothing; and then send the string ATDT5551212 to dial the telephone. The expected
string is CONNECT. If the string CONNECT is received the remainder of the script is executed. In addition the
ible. For instance, with the following script:
ABORT 'BUSY'
ABORT 'NO CARRIER'
OK\r\n ATD1234567
\r\n \c
ECHO ON
CONNECT \c
ogin: account
all output resulting from modem configuration and dialing is not visible, but starting with the CONNECT (or
BUSY) message, everything will be echoed.
HANGUP
The HANGUP options control whether a modem hangup should be considered as an error or not. This option is
useful in scripts for dialling systems which will hang up and call your system back. The HANGUP options can
be ON or OFF.
When HANGUP is set OFF and the modem hangs up (e.g., after the first stage of logging in to a callback sys‐
tem), chat will continue running the script (e.g., waiting for the incoming call and second stage login
prompt). As soon as the incoming call is connected, you should use the HANGUP ON directive to reinstall normal
hang up signal behavior. Here is an (simple) example script:
ABORT 'BUSY'
OK\r\n ATD1234567
\r\n \c
CONNECT \c
'Callback login:' call_back_ID
HANGUP OFF
ABORT "Bad Login"
'Callback Password:' Call_back_password
TIMEOUT 120
CONNECT \c
HANGUP ON
ABORT "NO CARRIER"
ogin:--BREAK--ogin: real_account
etc ...
TIMEOUT
The initial timeout value is 45 seconds. This may be changed using the -t parameter.
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
This will change the timeout to 10 seconds when it expects the login: prompt. The timeout is then changed to 5
seconds when it looks for the password prompt.
The timeout, once changed, remains in effect until it is changed again.
SENDING EOT
The special reply string of EOT indicates that the chat program should send an EOT character to the remote.
This is normally the End-of-file character sequence. A return character is not sent following the EOT. The
EOT sequence may be embedded into the send string using the sequence ^D.
\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 charac‐
ters 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.)
ENVIRONMENT VARIABLES
Environment variables are available within chat scripts, if the -E option was specified in the command line.
The metacharacter $ is used to introduce the name of the environment variable to substitute. If the substitu‐
tion fails, because the requested environment variable is not set, nothing is replaced for the variable.
TERMINATION CODES
The chat program will terminate with the following completion codes.
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.
7 The fourth string marked as an ABORT condition occurred.
... The other termination codes are also strings marked as an ABORT condition.
Using the termination code, it is possible to determine which event terminated the script. It is possible to
decide if the string "BUSY" was received from the modem as opposed to "NO DIAL TONE". While the first event
may be retried, the second will probably have little chance of succeeding during a retry.
SEE ALSO
Additional information about chat scripts may be found with UUCP documentation. The chat script was taken from
the ideas proposed by the scripts used by the uucico program.
uucico(1), uucp(1)
COPYRIGHT
The chat program is in public domain. This is not the GNU public license. If it breaks then you get to keep
both pieces.
Chat Version 1.22 22 May 1999 CHAT(8)
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