Let me give you a little overview of what the following snippet of code is supposed to do: The script used to display the topics has two modes. If it's passed a topic ID through the topic parameter, it attempts to display that specific topic. If no parameters are passed to it, it displays a list of the topics available to read. The topic list is generated by listing all the files in the topic directory and extracting the title and author from those files. The topic IDs correspond to the names of the files in the topic directory. If the topic parameter is supplied, the full text of the topic is displayed. Each of the responses is displayed on the same page as the original topic, and a form used to respond to the topic is also displayed. The full source code appears below:

#!/usr/bin/perl

use CGI;
$query = new CGI;

$topic_directory = "topics";

if($query->param('topic')){
     $topic = $query->param('topic');
     &file_error unless (&open_topic);
     &format_error unless (&parse_topic);
     &print_page_start;
     &print_topic;
     &print_response_form;
     print "<P>Return to the <A HREF=\"display.pl\">Topic
list</A>.</P>\n";
     &print_page_end;
}
else{
     &page_title = "Topic Index";
     &print_page_start;
     &print_topic_index;
     &print_page_end;
}

sub print_page_start{
    print $query->header;

sub print_topic_index{
     eval{
     opendir(TOPICS, "$topic_directory")
          or die "Can't open $topic_directory";
     @topics = grep (/^.+\.txt$/, readdir (TOPICS));
     foreach $topic (@topics){
          $topic =~ s/(.+)\.txt/$1/;
          &open_topic;
          &parse_topic;
          print "<A HREF=\"display.pl?topic=$topic\">";
          print "$page_title</A>, $topic_author<BR>\n";
}
};
}
........
.......#<CODE HERE WAS OMITTED>
The following code contains the form that holds the variable contents 
+for
$topic   The problem that I am having is I do not understand how the t
+opic
parameter in the form is passed a topic ID when it is a hidden field? 
+ The
code for the form creation is below:


sub print_response_form{
     print "<FORM METHOD=\"post\" ACTION=\"post.pl\">\n";
     print "<INPUT TYPE=\"hidden\" NAME=\"action\" ";
     print "VALUE=\"response\">\n";
     print "<INPUT TYPE=\"hidden\" NAME=\"response_to\" ";
     print "VALUE=\"$topic\">\n";
     print "Author: ";
     print "<INPUT TYPE=\"text\" NAME=\"author\" ";
     print "SIZE=40 MAXLENGHT=72 VALUE=\"$author\"><BR>\n";
     print "Message body: <BR>\n";
     print "<TEXTAREA ROWS=10 COLS=60 NAME=\"post\";
     print "WRAP=\"virtual\">";
     print ".........
..................................
.
[download]

Again I just don't understand how the parameter is assinged its value? Can anyone help me with this?

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