c# - Why doesn't $ in .NET multiline regular expressions match CRLF?

Question

I have noticed the following:

var b1 = Regex.IsMatch("Line1
Line2", "Line1$", RegexOptions.Multiline);   // true
var b2 = Regex.IsMatch("Line1
Line2", "Line1$", RegexOptions.Multiline); // false

I'm confused. The documentation of RegexOptions says:

Multiline: Multiline mode. Changes the meaning of ^ and $ so they match at the beginning and end, respectively, of any line, and not just the beginning and end of the entire string.

Since C# and VB.NET are mainly used in the Windows world, I would guess that most files processed by .NET applications use CRLF linebreaks ( ) rather than LF linebreaks ( ). Still, it seems that the .NET regular expression parser does not recognize a CRLF linebreak as an end of line.

I know that I could workaround this, for example, by matching Line1 ?$, but it still strikes me as strange. Is this really the intended behaviour of the .NET regexp parser or did I miss some hidden UseWindowsLinebreaks option?

Answer 1

From MSDN:

By default, $ matches only the end of the input string. If you specify the RegexOptions.Multiline option, it matches either the newline character ( ) or the end of the input string. It does not, however, match the carriage return/line feed character combination. To successfully match them, use the subexpression ?$ instead of just $.

http://msdn.microsoft.com/en-us/library/yd1hzczs.aspx#Multiline

So I can't say why (compatibility with regular expressions from other languages?), but at the very least it's intended.