I needed this functionality recently and thought it could be done easily with regex. Google led me to http://www.regular-expressions.info/duplicatelines.html which said to sort the lines, and then search for the following:
and replace with:
Unfortunately, I couldn’t get this to work in EmEditor, even after enabling the option to search past line boundaries.
Can you add support for this type of regex to EmEditor ?
PS. I haven’t tried the macro yet, and am sure it works fine, but it would be nice if it could be done with regex.