Your code example contains a mix of HTML and Perl, what's up with that?

Now even after this, if i click the browser back button, the session still exists. I'm able to view the Page2.

Are you sure the browser isn't just showing you a cached version of the page? Many modern browsers now have "web developer tools", which you can use to see if your browser is actually making a request to the server or not. In any case, you can get your CGI script to kindly ask the browser not to cache the page, see e.g. here.

If you find that the session really does still exist, then have a closer look at the documentation and other threads on this matter. For example, you may want to call $session->flush() after delete; other places suggest that simply $session->clear() is enough - note that a session existing is not necessarily the same as a user being logged in within that session.

Are you sure the browser isn't just showing you a cached version of the page?
>> To confirm this i just created a hyperlink to Page4 on the logout page. On page4 also i had the script to check if a session exists or not.. i'm seeing the same session id on Page4 too.

You said you see the same session ID, which is not surprising since you're getting it from a cookie - or did you delete the cookie too? I think there is still some confusion here: Did you check if the session got deleted, such as by looking into the data store that holds the sessions, or by checking whether the session is empty or not? Also, are you equating a session existing with being logged in? Why do you need to delete the session, why isn't clearing it enough to effect the logout?

Here is my logout.pl script.

If the other two scripts aren't behaving, why blame the logout script?

Also, you're using CGI::Session directly which means you're not using a helper like CGI::Application ... which means you probably got that part wrong :)

see Re: reg access of stored session variable, Re^2: how do I force a specific session, not my own, to end?, cgi101, CGI, Re^7: Perl CGI -disabled, Mojolicious::Lite +and jQuery +AJAX + Mojo::Template, Re: HTML::Template not working

If the other two scripts aren't behaving, why blame the logout script?
>>If Logout script is working fine, then i should not see the same session id on the newly created Page4, right.

CGI::Session directly which means you're not using a helper like CGI::Application ... which means you probably got that part wrong :)
>>I don't see anything wrong in the script, i just followed the CPAN tutorial and crated this. Moreover i just need a simple script to logout the user by deleting a session.

If you're doing everything correctly, why is there a problem? Why can't you figure it out and fix it?

See CGI::Session "cache" issue/Re^3: CGI::Session "cache" issue where another person thinks CGI::Session isn't doing something correctly ... but at least he posted more code

You're not the first to say there is a problem with CGI::Session , see Re: ie with cgi::session not showing same session id which it was set and firefox doesn't show at all, but you haven't shown any code that proves/demonstrates/shows a problem with CGI::Session -- you have not shown enough code -- the problem is with your code

If you want to figure it out, check my links, try the debugging steps ... or post more code

One thing that you need to be careful to do, upon logout, is to break the user’s Back-button sequence.   You should be able to do this by sending him a redirect.

As others have suggested, it really helps to use a Perl framework that’s designed to do as much of the overall work as possible.   For example, http://www.cgi-app.org/index.cgi?LoginLogoutExampleApp has a complete example of a tiny CGI::Application site ...   It is fairly uncommon to see folks these days using CGI::Session directly.

The trouble is that Back will often hand you a cached copy of a previously displayed page.   But, the server is no longer in-sync with what it says:   the server now thinks that you have logged off, and, if you actually try to do anything with the cached page, you’ll discover that you have.   If you look at things using the debugger that’s built into your web browser, you’ll probably found that the web client didn’t send anything to the host when you pressed Back and it (merely) redisplayed the page.   You’ll probably find that you can go Back and Forward and see that, as you do, nothing new is being sent to the host.