Ptfilter.txt contains ptfilter.sed, a collection of filter routines to make it far easier to fine tune LilyPond's output where simple substitution can help.
Pie.txt contains a filter used in a script as an example. Such scripts can be run on a block of selected text in emacs-xemacs.
lyinclude is a python script (my first) which substitutes the content of included files for the \include command. It's to prepare a lilypond music file to send to someone else.
Octly.txt contains a sed command file which transposes up to seven octaves up or down according to how you mark up the file. For dos-win, sed is easy to get and all linux distributions have it.