为什么 .NET 多行正则表达式中的 $ 不匹配 CRLF？

Question

I have noticed the following:

var b1 = Regex.IsMatch("Line1\nLine2", "Line1$", RegexOptions.Multiline);   // true
var b2 = Regex.IsMatch("Line1\r\nLine2", "Line1$", 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 ( \\r\\n ) rather than LF linebreaks ( \\n ). 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\\r?$ , 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 (\\n) 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 \\r?$ 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.