Why doesn't my regular expression collapse groups of newlines?

Question

I have the following regex to try to reduce groups of newlines:

s/(\n|\r\n|\n\r)(\n|\r\n|\n\r)(\n|\r\n|\n\r)+/\n\n/gmi;

It started out as:

s/\n\n(\n)+/\n\n/gmi

I am looking to reduce the number of newlines that are continuous to a maximum of two in a row (just trying to do some cleanup on some files that I am importing for an internal wiki). The data has several lines of CRLF's spread throughout it (Windows data files). Yet, it doesn't seem to work.

What am I doing wrong? Here is a sample where it is coming out wrong:

Starts off as:

added missing options for Menu and toolbar positioning</p>

</div>

</body>

</html>

I am stripping HTML tags, so it ends up like this:

added missing options for Menu and toolbar positioning

Then I apply the regex and it comes out as:

added missing options for Menu and toolbar positioning

Answer 1

Try also matching any other whitespace left over around those newlines:

s/(\r?\n[ \t]*){2,}/\n\n/g;

Answer 2

did you try matching your multiple groups like this?

(\r\n){2,}/\n\n

Answer 3

Since you seem to be having trouble applying the answers given, maybe you could show us some of your actual data, with

use Data::Dumper;
$Data::Dumper::Useqq = 1;
print Dumper $slurped_file;

You may also want to try one pass removing any \r characters, and then your original newline-only substitution.

Answer 4

basically, what you need is:

s/(\r\n|\n\r|\n){3,}/\n\n/g;

Please notice the order of alternations - you have to start with the longest ones first.

Answer 5

Do you mean /s instead of /m?