NAME
chat - Automated conversational script with a modem
SYNOPSIS
chat
[
options
]
script
DESCRIPTION
The _c_h_a_t 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 (_p_p_p_d) and
the remote's _p_p_p_d process.
OPTIONS
-
-f _&_l_t_;_c_h_a_t _f_i_l_e_&_g_t_;_<_/_b_>
_<_d_d_>
_R_e_a_d _t_h_e _c_h_a_t _s_c_r_i_p_t _f_r_o_m _t_h_e _c_h_a_t _f_i_l_e. 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 _&_l_t_;_t_i_m_e_o_u_t_&_g_t_;_<_/_b_>
_<_d_d_>
_S_e_t _t_h_e _t_i_m_e_o_u_t _f_o_r _t_h_e _e_x_p_e_c_t_e_d _s_t_r_i_n_g _t_o _b_e _r_e_c_e_i_v_e_d_. _I_f _t_h_e _s_t_r_i_n_g
_i_s _n_o_t _r_e_c_e_i_v_e_d _w_i_t_h_i_n _t_h_e _t_i_m_e _l_i_m_i_t _t_h_e_n _t_h_e _r_e_p_l_y _s_t_r_i_n_g _i_s _n_o_t
_s_e_n_t_. _A_n _a_l_t_e_r_n_a_t_e _r_e_p_l_y _m_a_y _b_e _s_e_n_t _o_r _t_h_e _s_c_r_i_p_t _w_i_l_l _f_a_i_l _i_f _t_h_e_r_e
_i_s _n_o _a_l_t_e_r_n_a_t_e _r_e_p_l_y _s_t_r_i_n_g_. _A _f_a_i_l_e_d _s_c_r_i_p_t _w_i_l_l _c_a_u_s_e _t_h_e
_c_h_a_t program to terminate with a non-zero error code.
-
-r _&_l_t_;_r_e_p_o_r_t _f_i_l_e_&_g_t_;_<_/_b_>
_<_d_d_>
_S_e_t _t_h_e _f_i_l_e _f_o_r _o_u_t_p_u_t _o_f _t_h_e _r_e_p_o_r_t _s_t_r_i_n_g_s_. _I_f _y_o_u _u_s_e _t_h_e _k_e_y_w_o_r_d
_R_E_P_O_R_T, the resulting strings are written to this file. If this
option is not used and you still use _R_E_P_O_R_T keywords, the
_s_t_d_e_r_r 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 _E_C_H_O
keyword. When echoing is enabled, all output from the modem is echoed
to _s_t_d_e_r_r.
-
-E
-
Enables environment variable substitution within chat scripts using the
standard _$_x_x_x syntax.
-
-v
-
Request that the _c_h_a_t script be executed in a verbose mode. The
_c_h_a_t 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. SYSLOGs
are logged to facility LOG_LOCAL2.
-
-V
-
Request that the _c_h_a_t script be executed in a stderr verbose
mode. The _c_h_a_t 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 (to facility LOG_LOCAL2).
-
-T _&_l_t_;_p_h_o_n_e _n_u_m_b_e_r_&_g_t_;_<_/_b_>
_<_d_d_>
_P_a_s_s _i_n _a_n _a_r_b_i_t_r_a_r_y _s_t_r_i_n_g_, _u_s_u_a_l_l_y _a _p_h_o_n_e _n_u_m_b_e_r_, _t_h_a_t _w_i_l_l _b_e
_s_u_b_s_t_i_t_u_t_e_d _f_o_r _t_h_e _\_T _s_u_b_s_t_i_t_u_t_i_o_n _m_e_t_a_c_h_a_r_a_c_t_e_r _i_n _a _s_e_n_d _s_t_r_i_n_g_.
_<_d_t_>
_<_b_>_-_U _&_l_t_;_p_h_o_n_e _n_u_m_b_e_r _2_&_g_t_;_<_/_b_>
_<_d_d_>
_P_a_s_s _i_n _a _s_e_c_o_n_d _s_t_r_i_n_g_, _u_s_u_a_l_l_y _a _p_h_o_n_e _n_u_m_b_e_r_, _t_h_a_t _w_i_l_l _b_e
_s_u_b_s_t_i_t_u_t_e_d _f_o_r _t_h_e _\_U _s_u_b_s_t_i_t_u_t_i_o_n _m_e_t_a_c_h_a_r_a_c_t_e_r _i_n _a _s_e_n_d _s_t_r_i_n_g_.
_T_h_i_s _i_s _u_s_e_f_u_l _w_h_e_n _d_i_a_l_i_n_g _a_n _I_S_D_N _t_e_r_m_i_n_a_l _a_d_a_p_t_e_r _t_h_a_t _r_e_q_u_i_r_e_s _t_w_o
_n_u_m_b_e_r_s_.
_<_d_t_>
_<_b_>_s_c_r_i_p_t_<_/_b_>
_<_d_d_>
_I_f _t_h_e _s_c_r_i_p_t _i_s _n_o_t _s_p_e_c_i_f_i_e_d _i_n _a _f_i_l_e _w_i_t_h _t_h_e _-_f option then
the script is included as parameters to the _c_h_a_t program.
CHAT SCRIPT
The _c_h_a_t 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 _c_h_a_t 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 _c_h_a_t 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 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
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 cchhaatt to communicate with another
program, for example, a program to prompt the user and receive a
password typed in.
ABORT STRINGS
Many modems will report the status of the call as a string. These
strings may be CCOONNNNEECCTTEEDD or NNOO CCAARRRRIIEERR or BBUUSSYY. 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 BBUUSSYY while the next time it may receive NNOO CCAARRRRIIEERR.
These "abort" strings may be specified in the script using the _A_B_O_R_T
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 _O_K. When it receives _O_K,
the string ATDT5551212 to dial the telephone. The expected string is
_C_O_N_N_E_C_T. If the string _C_O_N_N_E_C_T is received the remainder of the
script is executed. However, should the modem find a busy telephone, it will
send the string _B_U_S_Y. 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 _N_O _C_A_R_R_I_E_R, it will abort
for the same reason. Either string may be received. Either string will
terminate the _c_h_a_t script.
CLR_ABORT STRINGS
This sequence allows for clearing previously set AABBOORRTT strings.
AABBOORRTT strings are kept in an array of a pre-determined size (at
compilation time); CCLLRR__AABBOORRTT will reclaim the space for cleared
entries so that new strings can use that space.
SAY STRINGS
The SSAAYY directive allows the script to send strings to the user
at the terminal via standard error. If cchhaatt 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.
SSAAYY 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 "Dialing 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
$ SAY "Logged in OK ...\n"
_e_t_c _._._.
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:
-
Dialing your ISP...
-
Waiting up to 2 minutes for connection ... Connected, now logging in ...
Logged in OK ...
REPORT STRINGS
A rreeppoorrtt 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 _R_E_P_O_R_T
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
_C_O_N_N_E_C_T. If the string _C_O_N_N_E_C_T 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
This sequence allows for clearing previously set RREEPPOORRTT strings.
RREEPPOORRTT strings are kept in an array of a pre-determined size (at
compilation time); CCLLRR__RREEPPOORRTT will reclaim the space for cleared
entries so that new strings can use that space.
ECHO
The echo options controls whether the output from the modem is echoed
to _s_t_d_e_r_r. This option may be set with the _-_e option, but
it can also be controlled by the _E_C_H_O keyword. The "expect-send"
pair _E_C_H_O _O_N enables echoing, and _E_C_H_O _O_F_F
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'
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 _C_O_N_N_E_C_T (or _B_U_S_Y) message, everything
will be echoed.
HANGUP
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 OONN or OOFFFF.
When HANGUP is set OFF and the modem hangs up (e.g., after the first
stage of logging in to a callback system), cchhaatt 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 HHAANNGGUUPP OONN directive to reinstall normal hang up
signal behavior. Here is an (simple) example script:
-
ABORT 'BUSY'
-
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
_e_t_c _._._.
TIMEOUT
The initial timeout value is 45 seconds. This may be changed using the --tt
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
The special reply string of _E_O_T 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 _B_R_E_A_K 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
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. 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
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,
_n_o_t_h_i_n_g is replaced for the variable.
TERMINATION CODES
The _c_h_a_t 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 _e_x_p_e_c_t 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 _A_B_O_R_T condition occurred.
-
5
-
The second string marked as an _A_B_O_R_T condition occurred.
-
6
-
The third string marked as an _A_B_O_R_T condition occurred.
-
7
-
The fourth string marked as an _A_B_O_R_T condition occurred.
-
...
-
The other termination codes are also strings marked as an _A_B_O_R_T
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.
COPYRIGHT
The _c_h_a_t program is in public domain. This is not the GNU public
license. If it breaks then you get to keep both pieces.