RequirementsThe following list outlines the recommended hardware, software, network infrastructure, and service packs that you will need:
- Microsoft Visual Basic .NET or Microsoft Visual Basic 2005
- An understanding of Visual Basic .NET or Visual Basic 2005
- A basic understanding of regular expression syntax
Using Regular Expressions to Match a Pattern
- Open Visual Studio .NET or Visual Studio 2005.
- Create a new Visual Basic .NET or Visual Basic 2005 Console Application.
- Use the Imports statement on the Text.RegularExpressions namespace so that you will not be required to qualify declarations in those namespaces later in your code. The Imports statement must be used prior to any other declarations:
- The string that we will compare against the regular expression pattern will be passed as a command-line argument. In Visual Basic .NET or in Visual Basic 2005, we need to call the GetCommandLineArgs method to retrieve the data passed in as a command-line argument. Add this code to the Main procedure in the Module1.
Dim Args As String() = System.Environment.GetCommandLineArgs()
- Define a new regular expression that will use a pattern match to validate an e-mail address. The following regular expression is structured to accomplish three things:
- Capture the substring before the @ symbol and put that into the "user" group.
- Capture the substring after the @ symbol and put that into the "host" group.
- Make sure that the first half of the string does not have an @ symbol.
Dim EmailRegex As Regex = New Regex("(?<user>[^@]+)@(?<host>.+)")
- Define a new string containing a valid e-mail address. This provides a default value if the method's command-line argument is empty:
Dim S As String = "email@example.com"
- Check to see if there are any command-line parameters; if there are, retrieve the first parameter and assign it to the variable "s".
If Args.Length > 1
S = Args(1)
- Use the Match method to pass in the e-mail address variable and return a new Match object. The Match object will return regardless of whether any matches were found in the source string.
Dim M As Match = EmailRegex.Match(S)
- By examining the Success property, we can decide whether to continue processing the Match object or to print an error message. If successful, display the "user" and "host" named groups within the Groups collection of the Match object.
Console.WriteLine("User: " & M.Groups("user").Value)
Console.WriteLine("Host: " & M.Groups("host").Value)
Console.WriteLine(s & " is not a valid email address")
- To keep the console window open after running the application, add the following lines of code:
Console.WriteLine("Hit <enter> to exit...")
- Build your project.
- To run the application in the development environment using the default e-mail address specified in the code, press F5 or click Start from the Debug menu. To start the application with a command-line argument, there are two options:
- Start a command window and navigate to the "bin" folder under the folder in which your project resides. Then type in the name of the executable followed by the e-mail address you wish to test.
- Locate the executable file for this project, and drag it to the Start...Run window on the taskbar. Add the e-mail address to verify, and click or press OK.
- Regular Expression Syntax
- Introduction to Regular Expressions
- Regular Expressions Language Elements (Microsoft .NET Framework General Reference)
- Regex Class (Microsoft .NET Framework Class Library)
- Regular Expressions as a Language (Microsoft .NET Framework Developer's Guide)
Article ID: 301264 - Last Review: May 13, 2008 - Revision: 1