A plethora of tools exist that operate as filters: they get data from a
source, operate on this data, and write possibly modified data to a
destination. In the Unix world, these tools can be chained using a
technique called pipelining, where the output of one filter is connected
to the input of another filter. Some non-Unix worlds are reported to
have similar provisions.

To create Perl modules for filter functionality seems trivial at first.
Just open the input file, read and process it, and write output to a
destination file. But for really reusable modules this approach is too
simple. A reusable module should not read and write files itself, but
rely on the calling program to provide input as well as to handle the
output.

Text::Filter is a base class for modules that have in common that they
process text lines by reading from some source (usually a file),
manipulating the contents and writing something back to some destination
(usually some other file).

This module can be used 'as is', but its real power shows when used to
derive modules from it.

-Anton
<tobez@FreeBSD.org>