ck4up is a small command-line utility, writen in ruby, primarily
intended for CRUX ports maintainers to watch http and ftp sites for
updates, but may also be useful for others.

ck4up scans through a configuration file, fetches the listed URLs
from the web, computes the md5sum of the page, and compares the
value with one stored in a gdbm database. If both differ a message
will be written to the standard output.

To improve performance, ck4up is multi-threaded. Regular expressions
can be applied to each page in the event that ck4up produces
repetitive diff messages. For example, if daily snapshots and a web
counter are on the same page. To simplify maintenance of the
configuration file, a kind of macro-expansion can be used.
