chat(8) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | CHAT SCRIPT | COMMENTS | SENDING DATA FROM A FILE | ABORT STRINGS | CLR_ABORT STRINGS | SAY STRINGS | REPORT STRINGS | CLR_REPORT STRINGS | ECHO | HANGUP | TIMEOUT | SENDING EOT | GENERATING BREAK | ESCAPE SEQUENCES | ENVIRONMENT VARIABLES | TERMINATION CODES | SEE ALSO | COPYRIGHT | COLOPHON

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

NAME         top

       chat - Automated conversational script with a modem

SYNOPSIS         top

       chat [ options ] script

DESCRIPTION         top

       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 Protocol Daemon (pppd) and
       the remote's pppd process.

OPTIONS         top

       -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.

       -E     Enables environment variable substitution within chat
              scripts using the standard $xxx syntax.

       -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 through the SYSLOG; 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 device. This device is usually the
              local console at the station running the chat or pppd
              program.

       -s     Use stderr.  All log messages from '-v' and all error
              messages will be sent to stderr.

       -S     Do not use the SYSLOG.  By default, error messages are
              sent to the SYSLOG.  The use of -S will prevent both log
              messages from '-v' and error messages from being sent to
              the SYSLOG.

       -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         top

       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 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 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 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 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 ssword: hello2u2

       This would be a better script than the simple one used earlier.
       This would look for the same login: prompt, however, 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.

COMMENTS         top

       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

SENDING DATA FROM A FILE         top

       If the string to send starts with an at sign (@), the rest of the
       string is taken to be the name of a file to read to get the
       string to send.  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 provides a way for chat to
       communicate with another program, for example, a program to
       prompt the user and receive a password typed in.

ABORT STRINGS         top

       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.

CLR_ABORT STRINGS         top

       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         top

       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, 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 return and line feed are needed in the string to be
       output, you must explicitly 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 "Connected, now logging in ...\n"
              ogin: account
              ssword: pass
              $ \c
              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         top

       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 to no 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         top

       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         top

       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 following 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         top

       The HANGUP options control whether a modem hangup should be
       considered as an error or not.  This option is useful in scripts
       for dialling 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 hang up signal behavior.  Here is an (simple) 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         top

       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 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         top

       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         top

       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 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         top

       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     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. 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(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.

       \N     Send a null 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 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
              contains spaces. The sequence 'HI TIM' and HI\sTIM are the
              same.

       \t     Send or expect a tab character.

       \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 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.)

ENVIRONMENT VARIABLES         top

       Environment variables are available within chat scripts, if  the
       -E option was specified in the command line. The metacharacter $
       is used to introduce the name of the environment variable to
       substitute. If the substitution fails, because the requested
       environment variable is not set, nothing is replaced for the
       variable.

TERMINATION CODES         top

       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 program as 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 terminated the script. It is possible to decide if the
       string "BUSY" was received 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.

SEE ALSO         top

       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 program.

       uucico(1), uucp(1)

COPYRIGHT         top

       The chat program is in public domain. This is not the GNU public
       license. If it breaks then you get to keep both pieces.

COLOPHON         top

       This page is part of the ppp (An implementation of the Point-to-
       Point Protocol (PPP)) project.  Information about the project can
       be found at ⟨https://ppp.samba.org/⟩.  If you have a bug report
       for this manual page, see
       ⟨https://github.com/paulusmack/ppp/issues⟩.  This page was
       obtained from the project's upstream Git repository
       ⟨https://github.com/paulusmack/ppp⟩ on 2021-06-20.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2021-06-19.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

Chat Version 1.22              22 May 1999                       CHAT(8)

Pages that refer to this page: pon(1)pppd(8)