Question

I’m looking for a regex to ensure that my string only contains \r\n for newline and not \r or \n.

Sample text without errors:
Hello,\r\n\r\nWelcome on board of our brand-new cruise line.\r\nKind regards

Sample text with errors:
Hello\r\r\nWelcom on board of our brand-new cruise line.\nKind regards

Thank you in advance!
Kind regards, Danny

Answer 1

Try this regex:

(\r[^\n])|([^\r]\n)

if it matches, your text contains a loose \r or \n
Note: if you put this in string you need to escape the \r\n twice. or even better put it in @ string like this @"(\r[^\n])|([^\r]\n)"

Edit: example:

using System;
using System.Text.RegularExpressions;
public class Test
{
        public static void Main()
        {
                Regex r = new Regex(@"(\r[^\n])|([^\r]\n)");
                string[] Test = { "Hello,\r\n\r\nWelcome on board of our brand-new cruise line.\r\nKind regards", 
                                         "Hello\r\r\nWelcom on board of our brand-new cruise line.\nKind regards" };

                foreach(string t in Test)
                {
                        System.Console.Write("\"{0}\" ", t.Replace("\r", "\\r").Replace("\n", "\\n"));
                        if(r.IsMatch(t))
                                System.Console.WriteLine("Is not ok");
                        else
                                System.Console.WriteLine("Is ok");
                }
        }
}

Output:

"Hello,\r\n\r\nWelcome on board of our brand-new cruise line.\r\nKind regards" Is ok
"Hello\r\r\nWelcom on board of our brand-new cruise line.\nKind regards" Is not ok

Link: http://ideone.com/mauNN