Shorten empty lines to one line c# Regex

Question

I have some text like

This is a line




This is other line







This is another line

How to get rid of those multi empty lines ?

What I want is

This is a line

This is other line

This is another line

\\s says that matches any whitespace character (spaces, tabs, line breaks) but I cannot figure out how to make multi empty line to just one empty line ?

Answer 1

Regex.Replace(input, @"(\r?\n\s*){2,}", Environment.NewLine + Environment.NewLine);

\\r being optional lets it work with Unix-style line terminators. The output will have Windows-style terminators, though.

\\s* allows it to match on lines that contain whitespace. (I had originally put in a ? here to make the match non-greedy, but that's not actually necessary and possibly detrimental in this case. In .NET regular expressions, \\s and . don't match newlines with the default RegexOptions .)

{2,} makes sure it will only match with two successive newlines separated only by whitespace.