Programming on the Web today can involve any of several technologies, but the Common Gateway Interface (CGI) has held its ground as the most mature method--and one of the most powerful ones--of providing dynamic web content. CGI is a generic interface for calling external programs to crunch numbers, query databases, generate customized graphics, or perform any other server-side task. There was a time when CGI was the only game in town for server-side programming; today, although we have ASP, PHP, Java servlets, and ColdFusion (among others), CGI continues to be the most ubiquitous...