chat - 和数据集沟通的指令稿

总览 SYNOPSIS

chat [ options ] script

描述 DESCRIPTION

chat 程式在電腦與數據機之間定義溝通交換事宜。它最主要的目的是用來在點對點協定的隱形程式 (pppd) 以及遠端的 pppd 程序之間建立連線。

选项 OPTIONS

-f <chat file>: 從 chat 檔案讀取 chat 指令稿。這個選項的使用與 chat 的令稿參數互斥(mutually exclusive)。使用者必須具有存取該檔案的讀取權。在檔案中允許多線(multiple lines)設定。應該要以空白或是橫向定位(horizontal tab)字元來分隔字串。
-t <timeout>: 對於所要接收的期待字串(expected string)設定逾時限制。如果在該時間限制內沒有接收到該字串的話那麼就不送出回覆字串(reply string)。可以送出一個變通(alternate)的回覆或者如果沒有變通的回覆字串則該指令稿將會失敗。一個失敗的指令稿將會使得 chat 程式以一個非零的錯誤碼結束。
-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 substituion within chat scripts using the standard $xxx syntax.
-v: 要求 chat 指令稿以冗長(verbose)模式執行。這個 chat 程式接下來會將所有從數據機接收的文字以及輸出的字串記錄到 SYSLOG 去。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 arbitary 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: script 如果指令稿沒有以 -f 選項指定在檔案裡那麼該指令稿會如同參數般被包含在 chat 程式裡。

CHAT 脚本 SCRIPT

chat 脚本定義通訊過程

一個指令稿裡包含一個或多個〞期待對方送出(expect-send)〞的配對字串(pairs of string)，以空白隔開，還有一個選擇性的〞期待對方送出之候補(subexpect-subsend)〞配對字串，以短線(dash)隔開。像下面這個例子：

: ogin:-BREAK-ogin: ppp ssword: hello2u2

這一行指示 chat 程式應該期待 "ogin:" 這個字串。如果在所分配的時間區間內接收簽入提示失敗的話，那它就送出一個中斷程序(break sequence)給遠端然後期待 "ogin:" 這個字串。如果第一個 "ogin:" 被接收到那麼中斷程序就不會產生。

一旦它接收到該簽入提示則 chat 程式將會送出 ppp 這個字串然後期待 "ssword:" 這個提示。當它接收到密碼提示以後，它將會送出密碼 hello2u2 。

一般在回覆字串後面會跟著送出一個機架返回(carriage return)。在〞期待〞字串裡除非以字元程序(character sequence)指定為必須否則不會期待它的出現。

期待程序(expect sequence)應該只包含辨認字串所需要的資料。因為它一般是儲放在磁碟檔案裡，它不應該包含變動的資訊。通常以期待字串來尋找時間字串(time strings)，網路辨識字串(network iden- tification strings)，或是其它變動的資料是不被接受的。

為求協助修正在初始化程序中(initial sequence) 可能會傳送錯誤的字元，所以尋找 "ogin:" 這個字串而不是 "login:" 。開頭的 "l" 字元可能接收錯誤而你永遠找不到該字串，即使它已經被系統送出。因此緣故，指令稿尋找 "ogin:" 而不是 "login:" 以及 "ssword" 而不是 "password:" 。

一個非常簡單的指令稿看起來可能像這樣：

: ogin: ppp ssword: hello2u2

換句話說，期待 ...ogin:, 送出 ppp, 期待 ...ssword:, 再送出 hello2u2 。

在實際使用上，簡單的指令稿是罕見的。最少最少，原先的字串沒有被接收時你應該要把候補期待(sub-sequences)包括進來。例如，考慮下面這個例子：

: ogin:--ogin: ppp ssword: hello2u2

這會是一個比前面所用的簡單指令稿更好的指令稿。這個會尋找相同同的 login: 提示，然而, 如果沒有接收到的話，會送出一個單獨的返回程序(return sequence)並且它會接著再次尋找 login: 。要是雜雜訊掩蓋掉第一個 login 提示那麼接著送出空線路(empty line)經常將會再次產生簽入提示。

COMMENTS

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 chat to communicate with another program, for example,
a program to prompt the user and receive a password typed in.

放弃字符串 ABORT STRINGS

許多數據機會以字串來回報呼叫的狀況。這些字串可能是 CONNECTED 或是 NO CARRIER
或是 BUSY 。通常要是數據機連線到遠端失敗的話應該會希望結束指令稿。困難是指令稿不會確實地知道它可能接收到哪個數據機字串。在某次嘗試時，他可能接收到
BUSY 然而下次它可能接收到 NO CARRIER 。

這些〞失敗〞字串可以用 ABORT 程序指定到指令稿中。像是下面這個例子般地寫到指令稿裡：

: ABORT BUSY ABORT 'NO CARRIER' '' ATZ OK ATDT5551212 CONNECT

這個程序將不會期待什麼；而且接著送出 ATZ 這個字串。對此期待的回應是 OK 這個字串。當它接收到 OK 時，字串 ADTD5551212
就進行撥號。期待字串是 CONNECT 。如果字串 CONNECT 被接收到那麼就會執行指令稿其餘的部份。然而，要是數據機發現電話忙線，他將會送出 BUSY
這個字串。這會使得該字串符合失敗字元程序(abort char- acter)。這個指令稿將會因為它發現一個失敗字串(abort
string)而失敗(fail)。如果他接收到的是 NO CARRIER 字串，它也會因為同樣的原因而失敗。不是可以接收到字串就是字串將終結 chat
指令稿。

CLR_ABORT STRINGS

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

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 explicitely
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 ...
ogin: account

ssword: pass
$ SAY "Logged in OK ... 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

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

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

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'

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

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'

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 ...

超时 TIMEOUT

初始的逾時值是 45 秒。這可以用 -t 參數來加以改變。

要對下一個期待字串改變逾時值的話，可以使用下面這個例子：

: ATZ OK ATDT5551212 CONNECT TIMEOUT 10 ogin:--ogin: TIMEOUT 5 assword:
hello2u2

這將會在期待 "login:" 提示的時候把逾時限制改成 10 秒。逾時限制接著在它尋找密碼提示時被改成 5 秒。

逾時限制一旦改變就會持續作用直到它再度被改變。

SENDING 发送 EOT

EOT 這個特別的回覆字串指示 chat 程式應該送出一個 EOT
字元到遠端去。這是一般的檔案結束(End-of-file)字元程序。在 EOT 後面並不會跟著送出一個返回字元(return)。這個 EOT 程序可以用
^D 序列嵌入到送出的字串裡。

產生中斷 GENERATING BREAK

BREAK 這個特別的回覆字串將會使得一個中斷情況被送出。
這個中斷是傳送端的一個特殊。接收端一般對此的處理是改變傳輸率。它可以用來循環測試遠端可能的傳輸率直到你能夠接到有效的簽入提示。
這個中斷程序可以用
\K 序列嵌入到送出的字串裡。

转义序列 ESCAPE SEQUENCES

期待以及回覆字串可以包含转义序列。所有這種程序在回覆字串中都是合法的。有許多在期待字串中是合法的。
那些在期待程序中無效的會被指出。

'': 期待或送出一個空字串(null string) 。如果你送出一個空字串那麼它還會送出一個返回字元。這個程序可以是一對省略符
號(apostrophe)或者也可以是引用字元。
\\b: 代表一個退位(backspace)字元。
\\c: 抑制在回覆字串結尾的新列(newline)字元。這是送出沒有返回字元尾隨的字串的唯一方法。它必須在送出字串的結尾。例如，這個程序 hello
將會簡單地送出字元 h, e, l, l, o。（在期待字串中無效。）
\\d: 延遲一秒鐘。該程式使用最長延遲為一秒的 sleep(1) 。（在期待字串中無效。）
\\K: 插入一個中斷（在期待字串中無效。）
\\n: 送出一個新列(newline)或換行(linefeed)字元。
\\N: 送出一個空字元(null character)。同樣的程序可以用代替。（在期待字串中無效。）
\\p: 暫停一小段時間。延遲 1/10 秒。（在期待字串中無效。）
\\q: 抑制字串寫往 SYSLOG 檔案。該 ?????? 字串被記錄到自己的空間。（在期待字串中無效。）
\\r: 傳送或期待一個機架返回（字元）
\\s: 代替字串中的空白。這個可以用在不願引用包含空白的字串之時。'HI TIM' 以及 HITIM 是相同的。
\\t: 傳送或期待一個定位(tab)字元。
\\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.)
\\\\: 傳送或期待一個倒斜線(backslash)字元。
\\ddd: 將八進位數字 (ddd) 折疊(collapse)成單一的 ASCII 字元並將其送出。（某些字元在期待字串中無效。）
^C: 替換含有以 C 代表之控制字元的程序。例如，字元 DC1(17) 是以 ^Q 表示。（某些字元在期待字串中無效。）

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 substition fails, because the requested environment
variable is not set, nothing is replaced for the variable.

TERMINATION CODES

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.