Simple Answer: No.

Lengthly Answer: You don't really want to do this, though at first you might think that you do. Ask yourself the question of what if the user has a 'flakey' network connection? People still use modems & some backwoods phone networks still drop you to lower baud rates, etc... What if the connection simply wasn't properly made? What if they're hitting BACK for a reason? NO,nonononono. You don't want to even TRY this.

Further, you'd be messing with the average surfer's normal procedure of 'doing their thing.' That's a great way to become unpopular fast. Don't try to outguess your users & treat them like they're stupid. (even if they are)

They real way to do this is to have the server see what they're doing, anticipate it, & deal with it gracefully.

Exception to the rule:So you're dead set on doing this huh?... Simple. Open a new browser window. There will be nothing to go BACK to...

The usual way to deal with this problem is to use a session number.

• the form is generated by a CGI script, it includes a (hidden) param that identifies the session (a unique number),
• received session numbers (and possibly session information) are stored in either a DB or in a flat file (be sure that file is properly locked by using the technique described in RE: File Locking),
• when you receive a new request you can then query the DB, or lock the session archive file and load it, to check that this is the first time that this session is sent to you. If not you can either discard the info or send back a message to the user.

And of course you can also look at merlyn's Linux Magazine Column (the last one on the page) that deals with this kind of problem.

#!/usr/local/bin/perl -w
use strict;
use CGI qw(:standard);

my @pnames;

if (@pnames = param()) {
   eval_answers();
   print_redirect();
} else {
   print header;
   print_my_top();
   print_name_table();
   print_my_bottom();
   print end_html;
}

exit();

# add sub routines here for what you want to do...

sub print_redirect {
   print "Status: 301 MOVED PERMANENTLY\n";
   print 'Location: http://www.some_isp.com/~mylogin/my_most_excellent
+_cgi.cgi';
   print "\n";
   print "\n";
}
[download]

Justin Eltoft

"If at all god's gaze upon us falls, its with a mischievous grin, look at him" -- Dave Matthews

The key thing is that while there is JS code that can disable a back button, there are always ways around it (such as through menu options, key shortcuts, off-beat browsers that don't support such mis-features, etc). It's better to fix the problem on the server side than on the browser side where you have less control.

When the results are available, store them with the reference number.

If you get a request you've already dealt with, you can serve the results immediately, from your cache.

Any use to you?

Andy.

update: I re-read the question. I guess you'd only need to keep a list of 'used' reference numbers, not each actual results set.

ORYou could store an array with the last(or last 5, as above) users(assuming that there is some data as such on the form, i.e., unique data describing the user; name, email, etc.). Then, you could match the current user against the array(or scalar), and see if they match; if so, your response can be as above, or whatever suits your purposes.

These are just a few suggestions; there's more than one way to do it, but its hard to know without some more data.