| CHAT(8) | System Manager's Manual | CHAT(8) |
chat - 與數據機自動溝通的指令稿
chat [ options ] script
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。
chat 腳本定義通訊過程
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：
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：
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：
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 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:
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.
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：
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。
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, 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:
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:
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:
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 following script:
all output resulting from modem configuration and dialing is not visible, but starting with the CONNECT (or BUSY) message, everything will be echoed.
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:
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：
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。
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。
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。
期待以及回覆字串可以包含轉義序列。 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。
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.
The chat program will terminate with the following completion codes.
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.
關於 chat 指令稿的其它資訊可以在 UUCP 文件裡找到。chat 指令稿 的概念由 uucico 程式所使用的指令稿來的。
The chat program is in public domain. This is not the GNU public license. If it breaks then you get to keep both pieces.
asdchen <asdchen@pc2.hinet.net>
1995/09/30
http://cmpp.linuxforum.net
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| 22 May 1999 | Chat Version 1.22 |