RegexOptions.Multiline

This Regex option makes handling multiple lines easier. With it, we can apply a regular expression over an input string that has many lines.

Each line in the input string should be tested against the entire regular expression. To restate, a newline means a separate part of the string.

An example

We deal with specific control characters in the regular expression pattern. We can use the "^" char to specify the start of the input string, and "$" to specify the end of it.

using System;
using System.Text.RegularExpressions;

// Input string.
const string example = @"This string
has two lines";

// Get a collection of matches with the Multiline option.
MatchCollection matches = Regex.Matches(example, "^(.+)$", RegexOptions.Multiline);
foreach (Match match in matches)
{
    // Loop through captures.
    foreach (Capture capture in match.Captures)
    {
        // Display them.
        Console.WriteLine("--" + capture.Value);
    }
}
--This string
--has two lines

Notes, RegexOptions

We can use an enumerated constant with Regex methods. There are other RegexOptions you can consider. For complicate problems, a RegexOptions enum is often needed.

Summary

RegexOptions.Multiline is useful for treating each separate line in an input string as a separate input. This can make dealing with long input strings much easier.