CHAT(8) BSD System Manager's Manual CHAT(8)NAMEchat - automated conversational script with a modem
SYNOPSISchat [options] [script]
DESCRIPTION
The chat program defines a conversational exchange between the computer
and the modem. Its primary purpose is to establish a connection between
the Point-to-Point Protocol Daemon (pppd(8)) and the remote's pppd pro-
cess.
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 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 via syslog(3);
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 dev-
ice. This device is usually the local console at the station run-
ning the chat or pppd(8) program.
-s Use stderr. All log messages from -v and all error messages will
be sent to stderr.
-S Do not use syslog(3). By default, error messages are logged via
syslog(3). The use of -S will prevent both log messages from -v
and error messages from being logged via syslog(3).
-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.
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, separat-
ed 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 se-
quence is not generated.
Once it receives 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 possi-
ble 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:" rath-
er 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 very least, you
should include sub-expect sequences should the original string not be re-
ceived. 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. If one is 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
ABORT STRINGS
Many modems will report the status of the call as a string. These strings
may be CONNECT 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 re-
ceive. On one attempt it may receive BUSY, while the next time it may re-
ceive NO CARRIER.
These "abort" strings may be specified in the script using the ABORT se-
quence. 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 ex-
pected response to this is the string OK. When it receives OK, it sends
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(8), and pppd is
running as a daemon (detached from its controlling terminal), standard
error will normally be redirected to the file /etc/ppp/connect-errors.
SAY strings must be enclosed in single or double quotes. If carriage re-
turn and line feed are needed in the string to be output, you must expli-
citly 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 "\nConnected, now logging in ...\n"
ogin: account
ssword: pass
$ SAY "Logged in OK ...\n"
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 ...
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 do not 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 program 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 keyword. 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 fol-
lowing script:
ABORT 'BUSY'
ABORT 'NO CARRIER'
'' ATZ
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 dialing 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 hangup signal behavior. Here is
an example script:
ABORT 'BUSY'
'' ATZ
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.
The following example illustrates how to change the timeout value for the
next expect string:
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.
GENERATING BREAK
The special reply string of BREAK will cause a break condition to be
sent. The break is a special signal on the transmitter. The normal pro-
cessing on the receiver is to change the transmission rate. It may be
used to cycle through the available transmission rates on the remote un-
til 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 se-
quences are legal in the reply string. Many are legal in the expect
string. Those which are not valid in the expect sequence are so indicat-
ed.
'' Expects or sends a null string. If you send a null string then it
will still send the return character. This sequence may be a pair
of either 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 char-
acter. 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(3) to sleep for one
second. (Not valid in expect.)
\K Insert a BREAK. (Not valid in expect.)
\n Send a newline or linefeed character.
\N Send a NUL 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(3) 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 contain 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 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.)
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 pro-
gram was 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.
Using the termination code, it is possible to determine which event ter-
minated the script. It is possible to decide if the string "BUSY" was re-
ceived 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.
COPYRIGHT
The chat program is in the public domain. This is not the GNU public
license. If it breaks then you get to keep both pieces.
MirOS BSD #10-current September 27, 1997 6
