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>CHAT Scripts</TITLE
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><DIV
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><H1
><A
NAME="PPP-CHAT"
></A
>Chapter 56. CHAT Scripts</H1
><DIV
CLASS="TOC"
><DL
><DT
><B
>Table of Contents</B
></DT
><DT
><A
HREF="ppp-chat.html#PPP-CHAT-SCRIPT"
>Chat Script</A
></DT
><DT
><A
HREF="ppp-chat-abort.html"
>ABORT Strings</A
></DT
><DT
><A
HREF="ppp-chat-timeout.html"
>TIMEOUT</A
></DT
><DT
><A
HREF="ppp-chat-eot.html"
>Sending EOT</A
></DT
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>Escape Sequences</A
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><P
>The automated conversational scripting supported by the
<SPAN
CLASS="PRODUCTNAME"
>eCos</SPAN
> PPP package is a subset of the
scripting language provided by the <B
CLASS="COMMAND"
>chat</B
> command
found on most UNIX and Linux systems.</P
><P
>Unlike the <B
CLASS="COMMAND"
>chat</B
> command, the
<SPAN
CLASS="PRODUCTNAME"
>eCos</SPAN
> <CODE
CLASS="FUNCTION"
>cyg_ppp_chat()</CODE
>
function takes as a parameter a zero-terminated array of pointers to
strings. In most programs this will be defined by means of an
initializer for a static array, although there is nothing to stop the
application constructing it at runtime. A simple script would be
defined like this:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> static char *chat_script[] =
{
"ABORT" , "BUSY" ,
"ABORT" , "NO CARRIER" ,
"" , "ATD5551234" ,
"ogin:--ogin:" , "ppp" ,
"ssword:" , "hithere" ,
0
}; </PRE
></TD
></TR
></TABLE
><P
>The following sections have been abstracted from the public domain
documentation for the <B
CLASS="COMMAND"
>chat</B
> command. </P
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="PPP-CHAT-SCRIPT"
>Chat Script</A
></H1
><P
> 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:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> "ogin:--ogin:" , "ppp" ,
"ssword:" , "hello2u2" ,
0 </PRE
></TD
></TR
></TABLE
><P
> This script fragment indicates that the
<CODE
CLASS="FUNCTION"
>cyg_ppp_chat()</CODE
> function should expect the
string "ogin:". If it fails to receive a login prompt within
the time interval allotted, it is to send a carriage return
to the remote and then expect the string "ogin:" again. If
the first "ogin:" is received then the carriage return is not
generated.</P
><P
> Once it received the login prompt the
<CODE
CLASS="FUNCTION"
>cyg_ppp_chat()</CODE
> function 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".</P
><P
> 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.</P
><P
> The expect sequence should contain only what is needed to
identify the string. 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.</P
><P
> 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:".</P
><P
> A very simple script might look like this:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> "ogin:" , "ppp" ,
"ssword:" , " hello2u2" ,
0 </PRE
></TD
></TR
></TABLE
><P
> In other words, expect "....ogin:", send "ppp", expect "...ssword:",
send "hello2u2".</P
><P
> In actual practice, simple scripts are rare. At the very least,
you should include sub-expect sequences should the original
string not be received. For example, consider the following
script:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> "ogin:--ogin:" , "ppp" ,
"ssword:" , "hello2u2",
0 </PRE
></TD
></TR
></TABLE
><P
> 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.</P
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