The chat command supports the following options:
-f <chat file>
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
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' (alternate reply) string can be sent.
Otherwise, 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 <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
the -r option is not used and you use the REPORT keyword, the
stderr file is used for the report strings.
Start with the echo option turned on. You turn echo on or
off at specific points in the chat script using the ECHO
keyword. When echoing is enabled, all output from the modem is echoed to
Enables environment variable substitution within
chat scripts using the standard $xxx syntax.
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)
2; the logging method is alterable using the -S
Request that the chat script be executed 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.
Use stderr. Log messages from -v and error
messages are sent to stderr.
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 <phone number>
Pass in an arbitrary string (usually a telephone number)
that will be substituted for the \T substitution metacharacter in a
-U <phone number 2>
Pass in a second string (usually a telephone 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
If the script is not specified in a file with the
-f option, the script is included as parameters to the chat
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
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 generated.
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 identification strings, or other variable pieces of data as
an expect string.
To correct for characters that are corrupted during the initial
sequence, look for the string "ogin:" rather than
"login:". The leading "l" character may be received in
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 interpreted 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, consider the following script:
ogin:--ogin: ppp ssword: hello2u2
This script is more effective than the simple one used earlier.
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
generate a login prompt again.
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
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.
Many modems report the status of a call as a string. These status strings are
often "CONNECTED" or "NO CARRIER" 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 CARRIER' '' ATZ OK ATDT5551212 CONNECT
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 CONNECT. If CONNECT
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 CARRIER string is received, it aborts for the same
The CLR_ABORT sequence clears previously set ABORT strings. ABORT strings are
kept in an array of a pre-determined size; CLR_ABORT reclaims the space for
cleared entries, enabling new strings to use that space.
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 controlling 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 OFF." For example, add a line similar to the following to
SAY "Dialing your ISP...\n"
SAY "Waiting up to 2 minutes for connection ..."
SAY "Connected, now logging in ...\n"
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 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 CONNECT 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:
The above sequence expects nothing, then sends the string
ATDT5551212 to dial the telephone. The expected string is CONNECT. If
CONNECT is received, the remainder of the script is executed. In addition,
the program writes the string CONNECT to the report file (specified by
-r) in addition to any characters that follow.
CLR_REPORT clears previously set REPORT strings. REPORT strings are kept in an
array of a pre-determined size; CLR_REPORT reclaims the space for cleared
entries so that new strings can use that space.
ECHO determines if modem output is echoed to stderr. This option may be
set with the -e option, but can also be controlled by the ECHO keyword.
The "expect-send" pair ECHO ON enables echoing, and ECHO OFF
disables it. With ECHO, you can select which parts of the conversation should
be visible. In the following script:
ABORT 'NO CARRIER'
All output resulting from modem configuration and dialing is not
visible, but output is echoed beginning with the CONNECT (or BUSY)
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 OFF. When HANGUP is set to OFF and the modem hangs up (for
example, following the first stage of logging in to a callback system),
chat continues running the script (for example, waiting 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 example of a simple script follows:
'Callback login:' call_back_ID
ABORT "Bad Login"
'Callback Password:' Call_back_password
ABORT "NO CARRIER"
The initial timeout value is 45 seconds. Use the -t parameter to change
the initial timeout value.
To change the timeout value for the next expect string, the
following example can be used:
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
Once changed, the timeout value remains in effect until it is
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
character is not sent following the EOT. The EOT sequence can embedded into
the send string using the sequence ^D.
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
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 expect a null string,
chat proceeds to the reply string without waiting. This sequence can be
a pair of apostrophes or quote mark characters.
Represents a backspace character.
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 example, the sequence
hello\c will simply send the characters h, e, l, l, o. (Not valid in
Delay for one second. The program uses sleep(1)
which delays to a maximum of one second. (Not valid in expect.)
Insert a BREAK. (Not valid in expect.)
Send a newline or linefeed character.
Send a null character. The same sequence may be
represented by \0. (Not valid in expect.)
Pause for 1/10th of a second. (Not valid in
Suppress writing the string to syslog. The string ??????
is written to the log in its place. (Not valid in expect.)
Send or expect a carriage return.
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.
Send or expect a tab character.
Send the phone number string as specified with the
-T option. (Not valid in expect.)
Send the phone number 2 string as specified with the
-U option. (Not valid in expect.)
Send or expect a backslash character.
Collapse the octal digits (ddd) into a single ASCII
character and send that character. (\000 is not valid in an expect
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.)
The chat program terminates with the following completion codes:
Normal program termination. Indicates that the script was
executed without error to normal conclusion.
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 properly executed.
An error occurred during the execution of the program.
This may be due to a read or write operation failing or chat receiving
a signal such as SIGINT.
A timeout event occurred when there was an expect string
without having a "-subsend" string. This 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.
The first string marked as an ABORT condition
The second string marked as an ABORT condition
The third string marked as an ABORT condition
The fourth string marked as an ABORT condition
The other termination codes are also strings marked as an
To determine which event terminated the script, use the
termination 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