Telnet script

telnet cannot be automated from within a script, except with special languages like expect, for obvious reason (see previous comment). Use ssh instead.

I agree with both of the prior comments and would add the following...

Q: Why would you want to non-interactively telnet to another system?

If you are wanting to run a command - then the rsh utility is what you should use (there are security implications with this - which is why both of the other experts have suggested ssh).

We could give you much better help if we could appreciate what your ultimate objective is.

I have done similar for talking to the METAR databases in order to pull down dynamic weather content for websites, typically in perl or expect.

If this is the type of thing that you are doing then you may be able to use netcat (works the same as cat - but over a network).

kind Regards,
Festive

I agree with the above comments on security, but it IS possible to script telnet...

(sleep 3; echo username; sleep 3; echo password; sleep 5; echo "ls -l"; sleep 3; echo "exit") | telnet hostname

Of course, this creates ANOTHER security hole as your userid and password for the remote system are in the script - So the script must only be readable by the owner. The "echo" commands do not appear to be visible if you do  `ps`, but this may not be true for all Unices.

rsh is better, if well managed. ssh is better still.

The author of this post does not endorse the information herein and accepts no resonsibility for any loss etc. YMMV, caveat emptor etc.

tfewster, could you please tell me which OS, which OS version, and which telnet version you tested this. I'm interested.

HP-UX 11.0 & ksh; I don't know the telnet version, but it's the "standard" version that comes with HP-UX.

I've used a similar trick with HP-UX 10.20 in the past, to manage routers, print servers etc. that allow telnet login but can't be managed _from_Unix_ any other way. For example, the Intel ISDN router has a nice Windows GUI management program (which is useless if you're dialled into the network via a 9600 baud modem :-) and a telnet interface. I had a cron job to enable the router, transfer data to a bank, then disable the router again for security.

From your comment, I take it Solaris/AIX/Linux don't allow this?

I would not use telnet to do this kind of job. A sniffer can capture the plain text package from a telnet connetion including user + password. ssh can do the job.

tfewster, just for your interested. The telnet in HP-UX have some other security problem as well, please go to the HP IT resource center to download the patch for your OS.
eg : PHNE_26096, PHNE_26771 for HP-UX 11.x, and you can get them for 10.x as well.

Thanks, yuzh - I agree that telnet is weak, but our IT security team are confident that no outsiders can access our network. That just leaves us with disgruntled, skilled employees to worry about (?!). We are currently testing a secure login server setup based around ssh.

The latest patch sets we have on our 50+ HP-UX systems is September 2001, plus a few "fix on fails". Our organisation does not have a regular patching programme, as all the applications would have to be re-tested and the application support teams don't have time to do that (even though we have dedicated servers for pre-production testing).

Incidentally, I tried the "trick" on AIX 4.3.3 and (with a bit of modification) it worked:

#!/usr/bin/ksh
#filename: commands.ksh
sleep 3; echo username; sleep 3; echo password; sleep 5; echo "ls -l"; sleep 3; echo "exit"

>./commands.ksh | telnet hostname

I'm happy not to have such telnet on Solaris/AIX/Linux/*BSD/IRIX ;-)
But have heard that such a buggy telnet comes with RH too :-(

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tfewster
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