Shell Programming and Scripting

Thanks in advance!!! Can I get someone to write this small script or can you direct me to a web link, etc. to get it done?
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Initiate this script every 15 - 20 secs or so through cron.

Gather LAN users' $info(username, mac or ipaddr, PID) OBJECT: Tie each username to a mac or ipaddr,
Write $info(3 pieces) for each logged-on user to a $file,
Open this $file for reading,
While not EOF,
Compare each line of $info(ipaddr or mac) looking for an ipaddr or mac match/duplication
if a ipaddr or mac match, check to see if the $username is the same
if the $username DO NOT match
Provide a warning, if possible, to these $usernames(on the same ipaddr/mac),
Kill both process of these $usernames(on the same ipaddr/mac).
else{}
else{}
rm $file
End
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Thank you!

What have you written so far and where are you stuck?

Some details about your OS, version, etc. would not hurt too.

Right now, the way you presented your problem it looks like homework and asking homework questions is forbidden by the rules. How about persuading us that this is not the case?

bakunin

Thanks for the reply. Unfortunately, I'm not a shell-script coder (compiled languages mostly).

In fact, I am the Comp. Sci. teacher of about 140 HS students. I am running Ubuntu LTS 8.01.2. I allow my students 2 ssh logins ( /etc/security/limits.conf ). This way they can see previous work they have coded, highlight a selection, paste it in the other shell(new work). Why re-invent the wheel for every lesson?

What I am trying to avoid is two(2) different users sharing work via the same process!!! If two different users are using the same terminal, shut them down! I must shut this "cheating" process down!!!! Imagine, my students can only learn by doing work, not from copying others efforts.

Thanks again!!!

Ok, accepted. But (i hope you don't mind) instead of writing a shell script for you i would like to challenge your premise:

Your intention is to prevent users from exchanging work. Alas, as long as you do not take addional measures your concept is not going to work because users could simply share files via publicly accessible directories: copy a file with your work to /tmp, chmod it to 777 and every user could copy it.

Even if this would be prevented somehow you could always exchange work through network-like connections (for instance the "talk" utility, "mail", etc.).

IMHO you need a chrooted environment (see "man chroot") for every student to effectively prevent exchange of work and in this case you could lift the 2-sessions limit because it is an artificial restraint then superfluous.

I hope this helps.

bakunin

Thank you bakunin! Already got this covered!! Students/users are in a chrooted jail and can use only lshell as their shell. It limits the commands they can enter(only: --help,ls,pwd,rm,mkdir,g++,java,javac,vim,clear, firefox[ssh -X]) and they can only see/navigate in their own directory. They do not have access to any public area(/home/jail/tmp) or other, except thru firefox(which I've rewritten restricting them greatly) to which they can access http://mylocalserver, where lessons are located. Still need the script here. I've been on this goal for 4+ years. I need this script made!!!

Thank you bakunin!! I have the students locked into a jail and also have lshell as the only shell they have access to. The lshell limits(by config) the commands they can use(--help,clear,ls,mkdir,rm,g++,java,javac,./,vim,mv,cp, and firefox). I have re-written firefox limiting them to http://mylocalwebserver where I have lessons for them. Their access is by "ssh -X user@myserver". They cannot see others or the file structure and are locked in by lshell's command limits. They have no mail, talk, etc. available to bypass the setup. Pretty cool. I just need a script to accomplish this goal I've stated.
OBJECTIVE:
What I am trying to avoid is two(2) different users sharing work via the same process!!! If two different users are using the same terminal, shut them down! I must shut this "cheating" process down!!!! Imagine, my students can only learn by doing work, not from copying others efforts.

Thanks again!!!

Thank you everyone for your help! I got an answer in the form of a script at:
When using ssh: limit the number of users, that can log on, per IP address -rate - Page 2 - LinuxQuestions.org
It works perfectly. I thought it might be of use to others. Maybe not.