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   # Create a random session ID number:
   my $sessionid = join "", map { int rand 100 } 1..20;
...
   print "Content-type: text/html\nSet-Cookie: session=$sessionid\n\n"
+;
   # And remember on the server which session that is:
   storesessioninfo($sessionid, $username, %other_session_info);

   if ($ENV{HTTP_COOKIE} =~ /sessionid=(\w+)/) {
      # Call the routine that reads the server-side session info:
      ($username, %other_session_info) = getsessioninfo($1); 
   }