chat.8

经典的ppp程序

.\" -*- nroff -*-
.\" manual page [] for chat 1.8
.\" $Id: chat.8,v 1.9 1999/09/06 05:10:23 paulus Exp $
.\" SH section heading
.\" SS subsection heading
.\" LP paragraph
.\" IP indented paragraph
.\" TP hanging label
.TH CHAT 8 "22 May 1999" "Chat Version 1.22"
.SH NAME
chat \- Automated conversational script with a modem
.SH SYNOPSIS
.B chat
[
.I options
]
.I script
.SH DESCRIPTION
.LP
The \fIchat\fR 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 (\fIpppd\fR) and
the remote's \fIpppd\fR process.
.SH OPTIONS
.TP
.B -f \fI<chat file>
Read the chat script from the chat \fIfile\fR. 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.
.TP
.B -t \fI<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
\fIchat\fR program to terminate with a non-zero error code.
.TP
.B -r \fI<report file>
Set the file for output of the report strings. If you use the keyword
\fIREPORT\fR, the resulting strings are written to this file. If this
option is not used and you still use \fIREPORT\fR keywords, the
\fIstderr\fR file is used for the report strings.
.TP
.B -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 \fIECHO\fR
keyword. When echoing is enabled, all output from the modem is echoed
to \fIstderr\fR.
.TP
.B -E
Enables environment variable substituion within chat scripts using the
standard \fI$xxx\fR syntax.
.TP
.B -v
Request that the \fIchat\fR script be executed in a verbose mode. The
\fIchat\fR 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.
.TP
.B -V
Request that the \fIchat\fR script be executed in a stderr verbose
mode. The \fIchat\fR 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.
.TP
.B -s
Use stderr.  All log messages from '-v' and all error messages will be
sent to stderr.
.TP
.B -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.
.TP
.B -T \fI<phone number>
Pass in an arbitary string, usually a phone number, that will be
substituted for the \\T substitution metacharacter in a send string.
.TP
.B -U \fI<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.
.TP
.B script
If the script is not specified in a file with the \fI-f\fR option then
the script is included as parameters to the \fIchat\fR program.
.SH CHAT SCRIPT
.LP
The \fIchat\fR script defines the communications.
.LP
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:
.IP
ogin:-BREAK-ogin: ppp ssword: hello2u2
.LP
This line indicates that the \fIchat\fR 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.
.LP
Once it received the login prompt the \fIchat\fR 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.
.LP
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.
.LP
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.
.LP
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:".
.LP
A very simple script might look like this:
.IP
ogin: ppp ssword: hello2u2
.LP
In other words, expect ....ogin:, send ppp, expect ...ssword:, send hello2u2.
.LP
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:
.IP
ogin:--ogin: ppp ssword: hello2u2
.LP
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.
.SH COMMENTS
Comments can be embedded in the chat script. A comment is a line which
starts with the \fB#\fR (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:
.IP
# Now wait for the prompt and send logout string
.br
\'# ' logout
.LP

.SH 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 \fBchat\fR to communicate with another
program, for example, a program to prompt the user and receive a
password typed in.
.LP

.SH ABORT STRINGS
Many modems will report the status of the call as a string. These
strings may be \fBCONNECTED\fR or \fBNO CARRIER\fR or \fBBUSY\fR. 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 \fBBUSY\fR while the next time it may receive \fBNO CARRIER\fR.
.LP
These "abort" strings may be specified in the script using the \fIABORT\fR
sequence. It is written in the script as in the following example:
.IP
ABORT BUSY ABORT 'NO CARRIER' '' ATZ OK ATDT5551212 CONNECT
.LP
This sequence will expect nothing; and then send the string ATZ. The
expected response to this is the string \fIOK\fR. When it receives \fIOK\fR,
the string ATDT5551212 to dial the telephone. The expected string is
\fICONNECT\fR. If the string \fICONNECT\fR is received the remainder of the
script is executed. However, should the modem find a busy telephone, it will
send the string \fIBUSY\fR. 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 \fINO CARRIER\fR, it will abort
for the same reason. Either string may be received. Either string will
terminate the \fIchat\fR script.
.SH CLR_ABORT STRINGS
This sequence allows for clearing previously set \fBABORT\fR strings.
\fBABORT\fR strings are kept in an array of a pre-determined size (at
compilation time); \fBCLR_ABORT\fR will reclaim the space for cleared
entries so that new strings can use that space.
.SH SAY STRINGS
The \fBSAY\fR directive allows the script to send strings to the user
at the terminal via standard error.  If \fBchat\fR 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.
.LP
\fBSAY\fR 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 explicitely add them to your string.
.LP
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:
.IP
ABORT BUSY 
.br
ECHO OFF 
.br
SAY "Dialling your ISP...\\n" 
.br
\'' ATDT5551212 
.br
TIMEOUT 120
.br
SAY "Waiting up to 2 minutes for connection ... "
.br
CONNECT '' 
.br
SAY "Connected, now logging in ...\n"
.br
ogin: account
.br
ssword: pass
.br
$ \c
SAY "Logged in OK ...\n"
\fIetc ...\fR
.LP
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:
.IP
Dialling your ISP...
.br
Waiting up to 2 minutes for connection ... Connected, now logging in ...
.br
Logged in OK ...
.LP

.SH REPORT STRINGS
A \fBreport\fR 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.
.LP
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.