正则表达式多行奇怪的行为

Question

I have a string like this:

string text = "ext_bus      0  0/0/3/0.0      side         CLAIMED     INTERFACE    IDE Primary Channel\r\ntarget       0  0/0/3/0.0.0    tgt          CLAIMED     DEVICE       \r\ndisk         0  0/0/3/0.0.0.0  sdisk";

When I do a regex multiline search to get the text in ext_bus third column (0/0/3/0.0) and last column (IDE Primary Channel):

Regex regExp = new Regex(@"^ext_bus\s*[0-9]+\s*(?<HWPath>\S+).*\s{2,}(?<BusName>.*?)\r?$", RegexOptions.Multiline);

The first group is OK: "0/0/3/0.0"

But the second group is the next line!: "target 0 0/0/3/0.0.0 tgt CLAIMED DEVICE "

How can this be possible with Multiline (only one line), and how can I get the last column (the text at the end of the string after 2 or more whitespaces).

Answer 1

The short answer is that it is because the first .* in your regex matches up till the end of the first line, then the \\s{2,} matches the newline characters, then the (?<BusName>.*?) will match all of the second line.

Multiline mode means that ^ and $ match the start and end of a line, not just the start and end of the whole string.

Remove the .* and then <BusName> will be the rest of the text on the line after the whitespace following 0/0/3/0.0 .

Answer 2

Why do you use regex?

You can do it easily with split

string value = "ext_bus      0  0/0/3/0.0      side         CLAIMED     INTERFACE    IDE Primary Channel\r\ntarget       0  0/0/3/0.0.0    tgt          CLAIMED     DEVICE       \r\ndisk         0  0/0/3/0.0.0.0  sdisk";
char[] delimiters = new char[] {' ' }; // here you can add more seperaors
string[] parts = value.Split(delimiters, StringSplitOptions.RemoveEmptyEntries);
for (int i = 0; i < parts.Length; i++)
{
    Console.WriteLine(parts[i]);
}