An optional element in C# RegEx matching expression

How to make 'test2' an optional element in the following C# RegEx expression getting 'test1' value parsed out correctly when 'test2' element is missing?

 StringBuilder sb = new StringBuilder(); sb.AppendLine(" test1=123 any text in between "); sb.AppendLine(" some "); sb.AppendLine(" more "); sb.AppendLine(" text in between "); sb.AppendLine(" test2=456 "); sb.AppendLine(" test1=789 some text .. test2=012 "); Regex regex = new Regex(@"test1=(?<test1>(\d+))((.|\s)+?)(test2=(?<test2>(\d+)))"); MatchCollection matches = regex.Matches(sb.ToString()); foreach (Match match in matches) { Group test1 = match.Groups["test1"]; Group test2 = match.Groups["test2"]; System.Console.WriteLine("Test1 = {0}, Test2 = {1}", test1.Value, test2.Value); } 

Thank you.

@Oded - I reply here as I can't get comment formatted properly and as my reply is longer than allowed by StackOverflow comment text length:

Thank you. Proposed in your second reply RegEx expression results in the following output:

 Test1 = 123, Test2 = Test1 = 789, Test2 = 

It's not quite correct. And your first reply RegEx expression results in

 Test1 = 123, Test2 = 456 Test1 = 789, Test2 = 012 

test output. That's is correct.

But if I change

sb.AppendLine(" test1=789 some text .. test2=012 "); 

to

sb.AppendLine(" test1=789 some text .. test52=012 "); 

then the test result output will have just one line

Test1 = 123, Test2 = 456 

and I wanted it to be

 Test1 = 123, Test2 = 456 Test1 = 789, Test2 = 

in that case.

2 Answers

Qualify that the whole test2 group is optional:

@"test1=(?<test1>(\d+))((.|\s)+?)(test2=(?<test2>(\d+)))?" 

From MSDN - Regular Expression Language - Quick Reference:

? - Matches the previous element zero or one time.

add a ? after the element you want to be optional

.|\scan be replaced by . since . matches whitespace as well

To match newlines as well you have to pass Singleline option Regex regex = new Regex(@"test1=(?<test1>(\d+))((.)+?)(test2=(?<test2>(\d+)))?",RegexOptions.Singleline);

(The solution by Oded is does all this)