Bash Scripting

user99099099 · 01-21-2009, 11:34 PM

Hi,

I'm throwing together a small bash script that automates connecting to a
number of servers through SSH and would like to add an extra layer of
verification just for peace of mind.

Right now everything's stored in my .ssh/known_hosts file but just to be
safe, I want to have the script check for a prompt.

For example, if I do "ssh server_name" I would like the script to read in
the response / output of that command to see if it says "Are you sure you
want to continue connecting (yes/no)?" or if it says "[user@server ~]$".
Dependent upon the response, I could have an if statement evaluate it and
send the proper response whether it be "yes" or a sudo command.

Thanks in advance.

rizwanrafique · 01-22-2009, 02:18 AM

You could write a small script that does something like:

Code:

#!/bin/bash

echo "Readlly?"
read choice

if [ $choice == "Y" ]; then
    /usr/bin/ssh $1
fi

Let's say you call it /home/rizwan/tmp/my_ssh.

Do:

Code:

alias ssh='/home/rizwan/tmp/my_ssh'

And you should be ok. You can further enhance my_ssh by sending all its parameters to the real ssh command.

Probably there are better ways but I would do that :-)

chrism01 · 01-22-2009, 04:52 AM

Actually, I think the OP wants to check the output of the ssh cmd to see he gets the 'host key has changed, could be a MITM attack.... continue...' etc msg.
In which case, I'd suggest using Perl Net::Ssh module http://search.cpan.org/~ivan/Net-SSH-0.09/SSH.pm or Net::SSH::Perl.
Other options inc IPC::Open2, IPC::Open3

user99099099 · 01-22-2009, 11:12 PM

Yes chrism01, you're correct. That's what I was going for. I'll check into the Perl solution. I've never done any Perl development but now wouldn't be a bad time to learn. Thanks.

chrism01 · 01-23-2009, 04:32 AM

Well, here's a couple of links:
http://perldoc.perl.org/ - lang docs, examples, tutorials
http://www.perlmonks.org/?node=Tutorials - more tutorials