System Administration Commands chat(1M)
NAME
chat - automated conversational exchange tool
SYNOPSIS
chat [options] script
DESCRIPTION
The chat program implements a conversational text-based
exchange between the computer and any serial device, includ-
ing (but not limited to) a modem, an ISDN TA, and the remote
peer itself, establishing a connection between the Point-
To-Point Protocol daemon (pppd) and the remote pppd process.
OPTIONS
The chat command supports the following options:
-f Read the chat script from the chat
file. This option is mutually
exclusive with the chat script
parameters. You must have read access
to use the file. Multiple lines are
permitted in the file. Use the space
or horizontal tab characters to
separate the strings.
-t Set the timeout for the expected
string to be received. If the string
is not received within the time
limit, the reply string is not sent.
If specified, a 'subexpect' (alter-
nate reply) string can be sent. Oth-
erwise, if no alternate reply strings
remain, the chat script fails.. A
failed script will cause the chat
program to terminate with a non-zero
error code.
-r Set the file for output of the report
strings. If you use the keyword
REPORT, the resulting strings are
written to this file. If the -r
option is not used and you use the
REPORT keyword, the stderr file is
used for the report strings.
-e Start with the echo option turned on.
You turn echo on or off at specific
points in the chat script using the
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System Administration Commands chat(1M)
ECHO keyword. When echoing is
enabled, all output from the modem is
echoed to stderr.
-E Enables environment variable substi-
tution within chat scripts using the
standard $xxx syntax.
-v Request that the chat script execute
in a verbose mode. The chat program
logs the execution state of the chat
script as well as all text received
from the modem and output strings
sent to the modem. The default is to
log through syslog(3C) with facility
local2; the logging method is alter-
able using the -S and -s options.
-V Request that the chat script be exe-
cuted in a stderr verbose mode. The
chat program logs all text received
from the modem and output strings
sent to the modem to stderr. stderr
is usually the local console at the
station running the chat or pppd
program.
-s Use stderr. Log messages from -v and
error messages are sent to stderr.
-S Do not use syslog. By default, error
messages are set to syslog. This
option prevents log messages from -v
and error messages from being sent to
syslog.
-T Pass in an arbitrary string (usually
a telephone number) that will be sub-
stituted for the \T substitution
metacharacter in a send string.
-U Pass in a second string (usually a
telephone number) that will be sub-
stituted for the \U substitution
metacharacter in a send string. This
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System Administration Commands chat(1M)
is useful when dialing an ISDN termi-
nal adapter that requires two
numbers.
script If the script is not specified in a
file with the -f option, the script
is included as parameters to the chat
program.
EXTENDED DESCRIPTION
Chat Script
The chat script defines 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
The example indicates that the chat program should expect
the string "ogin:". If it fails to receive a login prompt
within the time interval allotted, it sends a break sequence
to the remote and then expects the string "ogin:". If the
first "ogin:" is received, the break sequence is not gen-
erated.
Upon receiving the login prompt, the chat program sends the
string "ppp" and then expects the prompt "ssword:". When the
password prompt is received, it sends 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 received data. Because it's stored on a disk
file, it should not contain variable information. Generally
it is not acceptable to look for time strings, network iden-
tification strings, or other variable pieces of data as an
expect string.
To correct for characters that are corrupted during the ini-
tial sequence, look for the string "ogin:" rather than
"login:". The leading "l" character may be received in
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error, creating problems in finding the string. For this
reason, scripts look for "ogin:" rather than "login:" and
"ssword:" rather than "password:".
An example of a simple script follows:
ogin: ppp ssword: hello2u2
The example can be intrepreted as: expect ogin:, send ppp,
expect ...ssword:, send hello2u2.
When login to a remote peer is necessary, simple scripts are
rare. At minimum, you should include sub-expect sequences in
case the original string is not received. For example, con-
sider the following script:
ogin:--ogin: ppp ssword: hello2u2
This script is more effective than the simple one used ear-
lier. The string looks for the same login prompt; however,
if one is not received, a single return sequence is sent and
then the script looks for login: again. If line noise
obscures the first login prompt, send the empty line to gen-
erate a login prompt again.
Comments
Comments can be embedded in the chat script. Comment lines
are ignored by the chat program. A comment starts with the
hash ("#") character in column one. If a # character is
expected as the first character of the expect sequence,
quote the expect string. If you want to wait for a prompt
that starts with a # character, write something like this:
# Now wait for the prompt and send logout string
'# ' logout
Sending Data From A File
If the string to send begins with an at sign ("@"), the
remainder of the string is interpreted as the name of the
file that contains the string. 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 enables
chat to communicate with another program, for example, a
program to prompt the user and receive a password typed in.
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Abort
Many modems report the status of a call as a string. These
status strings are often "CONECTED" or "NO CARIER" or
"BUSY." If the modem fails to connect to the remote, you can
terminate the script. Abort strings may be specified in the
script using the ABORT sequence. For example:
ABORT BUSY ABORT 'NO CARIER' '' ATZ OK ATDT5551212 CONECT
This sequence expects nothing and sends the string ATZ. The
expected response is the string OK. When OK is received, the
string ATDT5551212 dials the telephone. The expected string
is CONECT. If CONECT is received, the remainder of the
script is executed. When the modem finds a busy telephone,
it sends the string BUSY, causing the string to match the
abort character sequence. The script fails because it found
a match to the abort string. If the NO CARIER string is
received, it aborts for the same reason.
ClrAbort
The CLRABORT sequence clears previously set ABORT strings.
ABORT strings are kept in an array of a pre-determined size;
CLRABORT reclaims the space for cleared entries, enabling
new strings to use that space.
Say
The SAY string enables the script to send strings to a user
at a terminal via standard error. If chat is being run by
pppd and pppd is running as a daemon (detached from its con-
trolling terminal), standard error is normally redirected to
the /etc/ppp/connect-errors file.
SAY strings must be enclosed in single or double quotes. If
carriage return and line feed are required for the output,
you must explicitly add them to your string.
The SAY string can provide progress messages to users even
with "ECHO OF." For example, add a line similar to the fol-
lowing to the script:
ABORT BUSY
ECHO OF
SAY "Dialing your ISP...\n"
'' ATDT5551212
TIMEOUT 120
SAY "Waiting up to 2 minutes for connection ..."
CONECT ''
SAY "Connected, now logging in ...\n"
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ogin: account
ssword: pass
$ \c
SAY "Logged in OK ... \n"
This sequence hides script detail while presenting the SAY
string to the user. In this case, you will see:
Dialing your ISP...
Waiting up to 2 minutes for connection...Connected, now logging in...
Logged in OK ...
Report
REPORT is similar to the ABORT string. With REPORT, however,
strings and all characters to the next control character
(such as a carriage return), are written to the report file.
REPORT strings can be used to isolate a modem's transmission
rate from its CONECT string and return the value to the
chat user. Analysis of the REPORT string logic occurs in
conjunction with other string processing, such as looking
for the expect string. It's possible to use the same string
for a REPORT and ABORT sequence, but probably not useful.
Report strings may be specified in the script using the
REPORT sequence. For example:
REPORT CONECT
ABORT BUSY
ATDT5551212 CONECT
ogin: account
The above sequence expects nothing, then sends the string
ATDT5551212 to dial the telephone. The expected string is
CONECT. If CONECT is received, the remainder of the script
is executed. In addition, the program writes the string CON-
NECT to the report file (specified by -r) in addition to any
characters that follow.
ClrReport
CLREPORT clears previously set REPORT strings. REPORT
strings are kept in an array of a pre-determined size;
CLREPORT reclaims the space for cleared entries so that
new strings can use that space.
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Echo
ECHO determines if modem output is echoed to stderr. This
option may be set with the -e option, but can also be con-
trolled by the ECHO keyword. The "expect-send" pair ECHO ON
enables echoing, and ECHO OF disables it. With ECHO, you
can select which parts of the conversation should be visi-
ble. In the following script:
ABORT 'BUSY'
ABORT 'NO CARIER'
"" AT&F
OK\r\n ATD1234567
\r\n \c
ECHO ON
CONECT \c
ogin: account
All output resulting from modem configuration and dialing is
not visible, but output is echoed beginning with the CONECT
(or BUSY) message.
Hangup
The HANGUP option determines if a modem hangup is considered
as an error. HANGUP is useful for dialing systems that hang
up and call your system back. HANGUP can be ON or OF. When
HANGUP is set to OF and the modem hangs up (for example,
following the first stage of logging in to a callback sys-
tem), chat continues running the script (for example, wait-
ing for the incoming call and second stage login prompt).
When the incoming call is connected, use the HANGUP ON
string to reinstall normal hang up signal behavior. An exam-
ple of a simple script follows:
ABORT 'BUSY'
"" AT&F
OK\r\n ATD1234567
\r\n \c
CONECT \c
'Callback login:' callbackID
HANGUP OF
ABORT "Bad Login"
'Callback Password:' Callbackpassword
TIMEOUT 120
CONECT \c
HANGUP ON
ABORT "NO CARIER"
ogin:--BREAK--ogin: realaccount
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Timeout
The initial timeout value is 45 seconds. Use the -t parame-
ter to change the intial timeout value.
To change the timeout value for the next expect string, the
following example can be used:
''"AT&F
OK ATDT5551212
CONECT \c
TIMEOUT 10
ogin:--ogin: username
TIMEOUT 5
assword: hello2u2
The example changes the timeout to ten seconds when it
expects the login: prompt. The timeout is changed to five
seconds when it looks for the password prompt.
Once changed, the timeout value remains in effect until it
is changed again.
EOT
The EOT special reply string instructs the chat program to
send an EOT character to the remote. This is equivalent to
using ^D\c as the reply string. The EOT string normally
indicates the end-of-file character sequence. A return char-
acter is not sent following the EOT. The EOT sequence can
embedded into the send string using the sequence ^D.
BREAK
The BREAK special reply string sends a break condition. The
break is a special transmitter signal. Many UNIX systems
handle break by cycling through available bit rates, and
sending break is often needed when the remote system does
not support autobaud. BREAK is equivalent to using \K\c as
the reply string. You embed the break sequence into the send
string using the \K sequence.
Escape Sequences
Expect and reply strings can contain escape sequences. Reply
strings accept all escape sequences, while expect strings
accept most sequences. A list of escape sequences is
presented below. Sequences that are not accepted by expect
strings are indicated.
'' Expects or sends a null string. If you send a null
string, chat sends the return character. If you
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expect a null string, chat proceeds to the reply
string without waiting. This sequence can be a
pair of apostrophes or quote mark 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. This sequence
must be at the end of the send string. For exam-
ple, 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 delays 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 1/10th of a second. (Not valid in
expect.)
\q Suppress writing the string to syslog. 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. Can 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.
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\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
ASCI character and send that character. (\000 is
not valid in an expect string.)
^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 is specified on the command line. The meta-
character $ introduces the name of the environment variable
to substitute. If the substition fails because the requested
environment variable is not set, nothing is replaced for the
variable.
EXIT STATUS
The chat program terminates with the following completion
codes:
0 Normal program termination. Indicates that the
script was executed without error to normal con-
clusion.
1 One or more of the parameters are invalid or an
expect string was too large for the internal
buffers. Indicates that the program was not prop-
erly executed.
2 An error occurred during the execution of the pro-
gram. This may be due to a read or write operation
failing 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
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indicates that you may not have programmed the
script correctly for the condition or that an
unexpected event 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.
To determine which event terminated the script, use the ter-
mination code. It is possible to decide if the string "BUSY"
was received from the modem versus "NO DIALTONE." While the
first event may be retried, the second probably will not
succeed during a retry.
ATRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
ATRIBUTE TYPE ATRIBUTE VALUE
Availability SUNWpppdu
Interface Stability Evolving
SEE ALSO
sleep(1), uucp(1C), pppd(1M), uucico(1M), syslog(3C), attri-
butes(5)
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Additional information on chat scripts are available with
UCP documentation. The chat script format was taken from
scripts used by the uucico program.
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