What I do is have a "mode" for each stage.

The mode would be undef on first loading the page. Submitting the form would include a hidden field or whatever that said "mode is now 'secondstage'" and so on.

So the code ends up being two or three large blocks like this:

if($mode eq ''){
  # stuff that happens on the first page
}

if($mode eq 'secondstage'){
  # stuff that happens after the upload
}

if($mode eq 'finalstage'){
  # stuff that happens after their secondstage input
}

if($mode eq 'finished'){
  print "Thanks, we're done.";
}
[download]

“Every bit of code is either naturally related to the problem at hand, or else it's an accidental side effect of the fact that you happened to solve the problem using a digital computer.”
M-J D

I think the question is about maintaining the data structure between invocations of the script. For that, vinforget will need to look into session management. I use Apache::Session but there are plenty of other choices.

Thanks a bunch. This is exactly what I am looking for. Vince

Rather than executing a new if() statement for each mode, you might want to check out elsif() instead. This has the advantage that your script will exit quicker as it will not check every single if() statement to see if it is true or not. It will skip to the end of the if/elsif blocks once it has been satisfied in one of the conditionals. Your example would change to the following:

my $mode = param('mode');

# Main
if (not defined $mode) {
 # ...
}

# After upload
elsif ($mode eq 'secondstage') {
 # ...
}

# Final stage
elsif ($mode eq 'finalstage') {
 # ...
}
[download]

To create cleaner code, I tend to do something like this:

sub main {
 # Main page
}

sub secondstage {
 # After upload
}

sub finalstage {
 # final stage
}

sub _invalid {
 # Output error message: no such mode
}

my $modes = {
 ''          => \&main,
 secondstage => \&secondstage,
 finalstage  => \&finalstage,
 _invalid    => \&invalid
};

my $mode = param('mode');
$modes->{ exists $modes->{$mode} ? $mode : '_invalid' }->();
[download]

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Will using this strategy preserve the state of the script (i.e. contents of data strcutures) per new HTTP request. i.e. when I go from one mode to another will the global variables be reset? It seems like they will 'cause when you go through one mode the perl script will exit. i used CGI::Session to get around this problem. Thanks.