# config stuff:
  my $cfg = {
     refresh  => 300,
     interval => 5,
     };

# at some point later in the script:

  my $expires = strftime("Expires: %a, %d %b %Y %H:%M:%S GMT\n", 
    gmtime(time+60*$cfg->{interval}));

  print <<"EOF";
Content-Type: $content_type
Refresh: $cfg->{refresh}
Pragma: no-cache
Expires: $expires

EOF