Visual Basic .NET Find Multiple Words with One Search

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You can use this recipe for finding one of a list of words in a line. This recipe assumes both words are whole words surrounded by whitespace and that the list is a short one containing the words moo and oink.

[edit] code

Imports System
Imports System.IO
Imports System.Text.RegularExpressions
Public Class Recipe
    Private Shared _Regex As Regex = New Regex("\s+(moo|oink)\s+")
    Public Sub Run(ByVal fileName As String)
        Dim line As String
        Dim lineNbr As Integer = 0
        Dim sr As StreamReader = File.OpenText(fileName)
        line = sr.ReadLine
        While Not line Is Nothing
            lineNbr = lineNbr + 1
            If _Regex.IsMatch(line) Then
                Console.WriteLine("Found match '{0}' at line {1}", _
                    line, _
                    lineNbr)
            End If
            line = sr.ReadLine
        End While
        sr.Close()
    End Sub
    Public Shared Sub Main(ByVal args As String())
        Dim r As Recipe = New Recipe
        r.Run(args(0))
    End Sub
End Class

[edit] How It Works

A special character class, \b, allows you to easily search for whole words. This is an advantage because without doing a whole bunch of extra work you can make sure that a search for some- thing, for example, doesn’t yield unexpected matches such as somethings. You can break the regular expression shown here into the following:

Regular Expression Description
\s whitespace . . .
+ found one or more times . . .
(...) followed by something . . .
\s followed by whitespace . . .
+ that occurs one or more times.
The something here is another expression, moo|oink. This expression is as follows:
m an m, followed by . . .
o an o, then . . .
o an o . . .
or...
o an o, followed by . . .
i an i, then . . .
n an n, followed by...
k a k.

[edit] Variations

A useful variation of this recipe is to replace the \s+ combination, which matches specifically whitespace, with the word boundary character class \b.

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