in reply to File Filtering... Help

If your files aren't too big, then this might get you started. 

perl -0777 -e"print <stdin> =~ m[( \Q$ARGV[0]\E .*? \Q$ARGV[1]\E )]sxg
+" "#BG" "#EN" < yourinputfile >youroutputfile

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Note: The quoting will be different for *nix. Using 's instead of "s will probably work, and you may not need to quote your start and end strings depending upon what they contain and which shell you are using.

Examine what is said, not who speaks.
"Efficiency is intelligent laziness." -David Dunham
"When I'm working on a problem, I never think about beauty. I think only how to solve the problem. But when I have finished, if the solution is not beautiful, I know it is wrong." -Richard Buckminster Fuller
If I understand your problem, I can solve it! Of course, the same can be said for you.

In Section Seekers of Perl Wisdom