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<TITLE>The Answer Guy 50: Automated Login Around a Challenge Card</TITLE>
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<H4>"The Linux Gazette...<I>making Linux just a little more fun!</I>"</H4>
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<H4>By James T. Dennis,
<a href="mailto:linux-questions-only@ssc.com">linux-questions-only@ssc.com</a><BR>
LinuxCare,
<A HREF="http://www.linuxcare.com/">http://www.linuxcare.com/</A>
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<H3 align="left"><img src="../../gx/dennis/qbubble.gif"
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>Automated Login Around a Challenge Card</H3>
<p><strong>From Wayne Xin on Thu, 20 Jan 2000
</strong></p>
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Automated Login Around a Challenge Card
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<P><STRONG>
Sorry for the bold disturbance. I've been frustrated with this problem.
Hope you can point me to the right solution.
</STRONG></P>
<P><STRONG>
I have a battery based security card that changes my password for ISP
connection every minute. So I can't totally automate my login process
with a fixed password. Is there a place that talks about pausing in the
middle of a script for me to type in the password and then continuing to
capture the remotely assigned IP?
</STRONG></P>
<P><STRONG>
Appreciate your help.
<br>PS: I am talking linux 6.1 (X86) modem/ISP configuration
<IMG SRC="../../gx/dennis/smily.gif" ALT=":)"
height="24" width="20" align="middle">
</STRONG></P>
<BLOCKQUOTE><IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
HEIGHT="28" WIDTH="50" BORDER="0"
>
In the 'expect' scripting language you can
use an '<tt>interact</tt>' function with one or more "escape
patterns."
</BLOCKQUOTE>
<BLOCKQUOTE>
Here's an example:
</BLOCKQUOTE>
<blockquote><pre>#!/usr/bin/expect -f
spawn telnet "somehost"
expect "login:"
send "myname\r"
expect "enter key from your card:"
interact "\r" {
return
}
expect "success"
## continue with script
interact
</pre></blockquote>
<BLOCKQUOTE>
In this case we open a telnet to "somehost" and we
automate part of the login (waiting for a login:
prompt, sending a name, waiting for a sort of
password for your card).
</BLOCKQUOTE>
<BLOCKQUOTE>
The interesting part of this is where we have the
'interact' directive. In this case we interact
until an [Enter] key is entered and when we see that
escape sequence we execute some 'expect' code (in this
case all we're doing is executing the 'return' from
the interact to the rest of our script).
</BLOCKQUOTE>
<BLOCKQUOTE>
It's possible in 'expect' to have multiple "escape
sequences" or "macros" as options to the the '<tt>interact</tt>'
function. Each of these can have its own block of
'expect' code. These other bits of code can '<tt>spawn</tt>'
other programs that have their own nested '<tt>interact</tt>'
functions, etc.
</BLOCKQUOTE>
<BLOCKQUOTE>
Obviously (as I've shown) you can also have multiple
'<tt>interact</tt>' sessions in a script. (It should also be
obvious that you'll only get to the second and subsequent
sessions by using a '<tt>return</tt>' from each of the
preliminary '<tt>interact</tt>' invocations.
</BLOCKQUOTE>
<BLOCKQUOTE>
Most 'expect' syntax is derived from the TCL libraries
around which it is build. TCL is a language that was
designed to be embedded into other applications and
utilities and 'expect' is a utility which lets you
run interactive programs, connected to psuedo-terminals
and control them through its '<tt>expect</tt>', '<tt>send</tt>',
and related functions. The rest of the language is
TCL.
</BLOCKQUOTE>
<BLOCKQUOTE>
Anyway that's the easiest way that I know of to
do this under Linux. There's also an <tt>Expect.pm</tt>
PERL module. I haven't used it, but it should have
most of the same features.
</BLOCKQUOTE>
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<P> <hr> <P>
<H5 align="center"><a href="http://www.linuxgazette.com/copying.html"
>Copyright &copy;</a> 2000, James T. Dennis
<BR>Published in <I>The Linux Gazette</I> Issue 50 February 2000</H5>
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