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 Proto-
col 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.
-v Request that the chat script be executed in a ver-
bose mode. The chat program will then log the exe-
cution 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. This
option will not work properly if the stderr is
redirected to the /dev/null location as is the case
should pppd be run in the 'detached' mode. In that
case, use the '-v' option to record the session on
the SYSLOG device.
-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.
CHAT SCRIPT
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 fol-
lowing 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 dur-
ing 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, how-
ever, 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 pro-
gram. 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
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 difficulty 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.
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
This sequence will expect nothing; and then send the
string ATZ. The expected response to this is the string
OK. When it receives OK, 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. However, should the modem find a busy telephone,
it will send the string BUSY. This will cause the string
to match the abort character sequence. The script will
then fail because it found a match to the abort string. If
it received the string NO CARRIER, it will abort for the
same reason. Either string may be received. Either string
will terminate the chat script.
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 nor-
mally be redirected to the file /etc/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 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:
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 hidden.
For example, if the above script works, the user will see:
Dialling your ISP...
Waiting up to 2 minutes for connection ... Con-
nected, now logging in ...
Logged in OK ...
REPORT STRINGS
A report string is similar to the ABORT string. The dif-
ference 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 pro-
gram will write to the expect-file the string "CONNECT"
plus any characters which follow it such as the connection
rate.
CLR_REPORT STRINGS
This sequence allows for clearing previously set REPORT
strings. REPORT strings are kept in an array of a pre-
determined size (at compilation time); CLR_REPORT will
reclaim the space for cleared entries so that new strings
can use that space.
ECHO
The echo options controls whether the output from the
modem is echoed to stderr. This option may be set with the
-e option, but it can also be controlled by the ECHO key-
word. The "expect-send" pair ECHO ON enables echoing, and
ECHO OFF disables it. With this keyword you can select
which parts of the conversation should be visible. 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 system), 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 sec-
onds 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.
GENERATING BREAK
The special reply string of BREAK will cause a break con-
dition to be sent. The break is a special signal on the
transmitter. The normal processing on the receiver is to
change the transmission rate. It may be used to cycle
through the available transmission rates on the remote
until you are able to receive a valid login prompt. The
break sequence may be embedded into the send string using
the \K sequence.
ESCAPE SEQUENCES
The expect and reply strings may contain escape sequences.
All of the sequences are legal in the reply string. Many
are legal in the expect. Those which are not valid in the
expect sequence are so indicated.
'' Expects or sends a null string. If you send a null
string then it will still send the return charac-
ter. This sequence may either be a pair of apostro-
phe 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.
\\ 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.)
TERMINATION CODES
The chat program will terminate with the following comple-
tion codes.
0 The normal termination of the program. This indi-
cates 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 pro-
gram. 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.
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 pro-
gram.
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.