MirBSD manpage: chat(8)

CHAT(8)                  BSD System Manager's Manual                   CHAT(8)


     chat - automated conversational script with a modem


     chat [options] [script]


     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-


     -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

     -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

     -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.


     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

     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 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


     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:


     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.


     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.


     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 ...


     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.


     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.


     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


     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 ...


     The initial timeout value is 45 seconds. This may be changed using the -t

     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.


     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.


     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.


     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-

     ''      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.)


     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

     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.


     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.

MirBSD #10-current            September 27, 1997                             6

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