Visual Basic .NET Find Hexadecimal Numbers

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This recipe will limit the input to numbers and letters that are valid for hexadecimal representations.

code

Imports System
Imports System.IO
Imports System.Text.RegularExpressions
Public Class Recipe
    Private Shared _Regex As Regex = New Regex("^[0-9a-f]+$", _
        RegexOptions.IgnoreCase)
    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

How It Works

This recipe uses a simple character class to limit the input to digits and the letters a through f:

Regular Expression Description
^ the beginning of the line, followed by . . .
[0-9a-f] a character class that matches the digits zero through nine and the letters
\s a through f . . .
+ found one or more times . . .
$ the end of the line.

Alternatively, you can replace 0-9 in the character class with \d.

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