| CHAT(8) | System Manager's Manual | CHAT(8) |
chat - 与数据机自动沟通的指令稿
chat [ options ] script
chat 程式在电脑与数据机之间定义沟通交换事宜。 它最主要的 目的是用来在点对点协定的隐形程式 (pppd) 以及远端的 pppd 程序 之间建立连线。
chat 脚本定义通讯过程
一个指令稿里包含一个或多个〞期待对方送出(expect-send)〞的配对 字串(pairs of string)，以空白隔开，还有一个选择性的〞期待对方 送出之候补(subexpect-subsend)〞配对字串，以短线(dash)隔开。像 下面这个例子：
这一行指示 chat 程式应该期待 "ogin:" 这个字串。如果在所分配的 时间区间内接收签入提示失败的话， 那它就送出一个中断程序(break sequence)给远端然后期待 "ogin:" 这个字串。 如果第一个 "ogin:" 被接收到那么中断程序就不会产生。
一旦它接收到该签入提示则 chat 程式将会送出 ppp 这个字串然后期 待 "ssword:" 这个提示。当它接收到密码提示以后，它将会送出密码 hello2u2 。
一般在回复字串后面会跟著送出一个机架返回(carriage return)。在 〞期待〞字串里除非以 字元程序(character sequence)指定为必 须否则不会期待它的出现。
期待程序(expect sequence)应该只包含辨认字串所需要的资料。因为 它一般是储放在磁碟档案里，它不应该包含变动的资讯。 通常以期待 字串来寻找时间字串(time strings)， 网路辨识字串(network iden- tification strings)，或是其它变动的资料是不被接受的。
为求协助修正在初始化程序中(initial sequence) 可能会传送错误的 字元，所以寻找 "ogin:" 这个字串而不是 "login:" 。 开头的 "l" 字元可能接收错误而你永远找不到该字串， 即使它已经被系统送出。 因此缘故，指令稿寻找 "ogin:" 而不是 "login:" 以及 "ssword" 而 不是 "password:" 。
一个非常简单的指令稿看起来可能像这样：
换句话说， 期待 ...ogin:, 送出 ppp, 期待 ...ssword:, 再送出 hello2u2 。
在实际使用上，简单的指令稿是罕见的。最少最少， 原先的字串没有 被接收时你应该要把候补期待(sub-sequences)包括进来。例如，考虑 下面这个例子：
这会是一个比前面所用的简单指令稿更好的指令稿。 这个会寻找相同 同的 login: 提示，然而, 如果没有接收到的话， 会送出一个单独的 返回程序(return sequence)并且它会接著再次寻找 login: 。要是杂 杂讯掩盖掉第一个 login 提示那么接著送出空线路(empty line)经常 将会再次产生签入提示。
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.
许多数据机会以字串来回报呼叫的状况。 这些字串可能是 CONNECTED 或是 NO CARRIER 或是 BUSY 。 通常要是数据机连线到远端失败的话 应该会希望结束指令稿。 困难是指令稿不会确实地知道它可能接收到 哪个数据机字串。在某次尝试时， 他可能接收到 BUSY 然而下次它可 能接收到 NO CARRIER 。
这些〞失败〞字串可以用 ABORT 程序指定到指令稿中。像是下面这个 例子般地写到指令稿里：
这个程序将不会期待什么；而且接著送出 ATZ 这个字串。对此期待的 回应是 OK 这个字串。当它接收到 OK 时，字串 ADTD5551212 就进行 拨号。期待字串是 CONNECT 。 如果字串 CONNECT 被接收到那么就会 执行指令稿其余的部份。然而，要是数据机发现电话忙线， 他将会送 出 BUSY 这个字串。 这会使得该字串符合失败字元程序(abort char- acter)。 这个指令稿将会因为它发现一个失败字串(abort string)而 失败(fail)。如果他接收到的是 NO CARRIER 字串， 它也会因为同样 的原因而失败。不是可以接收到字串就是字串将终结 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:
初始的逾时值是 45 秒。这可以用 -t 参数来加以改变。
要对下一个期待字串改变逾时值的话，可以使用下面这个例子：
这将会在期待 "login:" 提示的时候把逾时限制改成 10 秒。 逾时限 制接著在它寻找密码提示时被改成 5 秒。
逾时限制一旦改变就会持续作用直到它再度被改变。
EOT 这个特别的回复字串指示 chat 程式应该送出一个 EOT 字元到远 端去。这是一般的档案结束(End-of-file)字元程序。 在 EOT 后面并 不会跟著送出一个返回字元(return)。
这个 EOT 程序可以用 ^D 序列嵌入到送出的字串里。
BREAK 这个特别的回复字串将会使得一个中断情况被送出。 这个中断 是传送端的一个特殊。接收端一般对此的处理是改变传输率。 它可以 用来循环测试远端可能的传输率直到你能够接到有效的签入提示。
这个中断程序可以用 \K 序列嵌入到送出的字串里。
期待以及回复字串可以包含转义序列。 所有这种程序在回复字串中都 是合法的。有许多在期待字串中是合法的。 那些在期待程序中无效的 会被指出。
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.
关于 chat 指令稿的其它资讯可以在 UUCP 文件里找到。chat 指令稿 的概念由 uucico 程式所使用的指令稿来的。
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 |