pextract.icn: Program to separate good and bad patterns

This program takes the name of a file containing tile specifications
on the command line.   Tiles to be extracted are entered from standard
input.  Extracted tiles are written to standard output.

Options:

     -b              replace selected tiles by blank tiles
     -d              delete selected tiles from specification file
     -c              copy selected tiles, do not blank or delete
                       them.  This is the default; -c overrides
                       -b and -d.