Anchors

The anchors ^ and $ match a particular position. By default:

^ has two context-dependent meanings: an anchor and a character class negator.

$ has two context-dependent meanings: an anchor and a replacement group denoter.

using System;
using System.Text.RegularExpressions;


class Program
{
    static void Main(string[] args)
    {

      Console.WriteLine (Regex.Match ("Javascript", "^[J]a"));       
      Console.WriteLine (Regex.Match ("C#", "[Cc]$"));               
    }
}

The output:

Ja

If you specify RegexOptions.Multiline or include (?m) in the expression:

• ^ matches the start of the string or line (directly after a \n).
• $ matches the end of the string or line (directly before a \n).

A new line in Windows is nearly always denoted with \r\n rather than just \n.

This means that for $ to be useful, you must usually match the \r as well, with a positive lookahead: (?=\r?$)

The positive lookahead ensures that \r doesn't become part of the result.

The following matches lines that end in ".txt":

using System;
using System.Text.RegularExpressions;


class Program
{
    static void Main(string[] args)
    {
     string fileNames = "a.txt" + "\r\n" + "b.doc" + "\r\n" + "c.txt"; 
     string r = @".+\.txt(?=\r?$)"; 
     foreach (Match m in Regex.Matches (fileNames, r, RegexOptions.Multiline)) 
       Console.Write (m + " "); 

    }
}

The output:

a.txt c.txt