using System;
using System.Text.RegularExpressions;
public class Example
{
public static void Main()
{
string pattern = @"(^\#{4}\s{1}[\d\D].*?[:]\s{2})\n\n(>[\d\D].*?\s{2})\n([\d\D].*?\s{2})";
string substitution = @"$1\n\n$2\n> $3\n> ";
string input = @"#### <u>Author name</u> writes in his 'Title of some Book/Essay/Article':
> First sentence with soft line breaks at the end.
Second sentence.
Third sentence.
Any number of sentences if there are any will follow — all need to be in quote blocks.
<Some other text not belonging to above author comes after empty line>.
";
RegexOptions options = RegexOptions.Multiline;
Regex regex = new Regex(pattern, options);
string result = regex.Replace(input, substitution);
}
}
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for C#, please visit: https://msdn.microsoft.com/en-us/library/system.text.regularexpressions.regex(v=vs.110).aspx