If PHP is compiled into Apache, you can use:
<?php virtual ("calendar/calendar.pl"); ?>
You may need to use the complete URI from the root directory. Eg.
<?php virtual ("/cgi-bin/calendar/calendar.pl"); ?>
If PHP is NOT compliled into Apache, you will have to read the output of calendar.pl with file() using the full URL (http://.../calendar.pl) and echo each line of the array. Eg.
<?php
$calendar = file("http://your-site.com/cgi-bin/calendar/calendar.pl");
while ( list($key, $line) = each( $calendar ) )
{
echo "$line";
}
?>
Dan O.