the 'original' string function?

[Emanuel Berg <incal@dataswamp.org>]

Okay, this is gonna be a challenge to most guys who have been
processing text for a long time.

So, I would like a command, function or script, 'original',
that takes a string STR and a text file TXT and outputs
a score, from 0 to 100, how _original_ STR is, compared to
what is already in TXT.

So if I do

$ original "This isn't just another party" comments.txt

this will score 0 if that exact phrase to the letter already
exists in comments.txt.

But it will score 100 if not a single of those words exists in
the file! Because that would be 100% original.

Those endpoints are easy. But how to make it score - say - 62%
if some of the words are present, mostly spelled like that and
combined in ways that are not completely different?

Note: The above examples are examples, other definitions of
originality are okay. That is not the important part now - but
can be as interesting a part, later.

I'm not sure what function can solve this but I'm sure it will
be very original!

-- 
underground experts united
https://dataswamp.org/~incal