This is another example of a peice of crap code and I'm getting sick and tired of seeing this garbage on the site.
Why paste a code you haven't even had the time to test?
This is FULL of problems like:
Your second while loop increases %o which is set initially to 0 and never used again.

inc = %o

needs to be

inc %o

and

while ($read(%%,w,$+(*,$read(%%,%'),*),%^) 

needs to be

while ($read(%%,w,$+(*,$read(%%,%'),*),%^))

and

($exists(%%))

needs to be

(!$exists(%%))

On top of all that your second while loop does nothing but write one line to the file.

There is not even code to actually look for matching aka identicle lines.

If you fix all the problems i listed that would keep it from even running, the only thing it would do right now is leave you with a file with one line, the last line and would message you saying it found # matchs where # is actually the number of lines in the file minuse one.

Forget the fact that even posting before you test is utterly stupid and even verges on beind rude this script is a joke.

A bad bad joke.

You should be tarred and feathered.