CHAT(8) MachTen Programmer’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 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.

-l <lock file>
Perform the UUCP style locking using the indicated
lock file.

If the file could not be created then the chat pro-
gram will fail. The lock file will be deleted only
if the chat program fails to perform the script for
any reason. If the script is successful the lock
file will be left on the disk. It is expected that
the lock file will be deleted when the pppd process
no longer wishes to use the serial device.

The use of a lock file with chat and pppd’s lock
option should not be used at the same time. They
are mutually exclusive options and will cause one
or the other program to fail to achieve the
required lock if you use both.

-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.

-v Request that the chat script be executed in a ver-
bose mode. The chat program will then log all text
received from the modem and the output strings
which it sends to the SYSLOG.

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 unlesscharacter
it is specifically requested by using the
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 ssowrd: 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.

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.

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 assowrd: 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
character. This sequence may either be a pair of
apostrophe or quote characters. b r e p r e s e n t s a b a c k s p a c e c h a r a c t e r .

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 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.

Send a null character. The same sequence may be
represented by . (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.

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 HIM 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.)

EXAMPLE
The first example shows the use of chat by pppd to connect
to a remote Unix site using a Hayes modem attached to the
serial port and using the hardware flow-control device
/dev/ttyfa. The chat script expects nothing, sends a
Hayes standard tone dial command with an local seven digit
phone number, expects a "CONNECT" response from the local
modem when the remote modem connection is established,
sends a carriage-return, expects the "(l)ogin:" prompt
from the remote getty process, sends the user name "ppp",
expects a "(P)assword:" prompt, and sends the password
"foobar" for the ppp account.

pppd -d connect ’chat -v "" ATDT5551212 CONNECT ""
ogin: ppp assword: foobar’ /dev/ttya

The second example shows the same connection using a Comm-
ToolBox device (/dev/cm.out) which takes care of the modem
auto-dialing aspect of the serial line conversation.

pppd -d connect ’chat -v "" "" ogin: ppp assword:
foobar’ /dev/cm.out

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.

Chat Version 1.8 17 April 1994 5