The HTTP protocol helps, as there is a "If-Modified-Since"
header. So, you could use LWP, create an user agent, and
an HTTP Request object, set the "If-Modified-Since" header,
do the request, and look at the return status of the response.
If the status is 304, the content hasn't changed. If the status is 200, the content has changed. For any other status,
see RFC 2068.
Abigail
Comment on Re: questions concerning using perl to monitor webpages
This is great in principle for truly static pages, but for CGI output the "If-modified-since" is, like, now. So it depends on what kind of pages you're going to fetch if this particular trick will work.