Imports System

Imports System.Collections.Generic

Imports System.Linq

Imports System.Text

Public Module Module1

    Private Delegate Function Transform(ByVal value As String) As String

    Private ReadOnly _transformations As New Dictionary(Of String, Transform)

​

    Public Sub Main()

        IO.File.WriteAllLines("test.txt", {"bob is cool", "john is cooler", "nothing in here matches"})

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        _transformations.Add("bob", Function(value) value.Replace("bob", "ray"))

        _transformations.Add("john", Function(value) value.Replace("john", "jane"))

​

        Dim strOutput As New StringBuilder()

        Dim lines() As String = IO.File.ReadAllLines("test.txt")

        For Each line In lines

            Dim transformation = _transformations.FirstOrDefault(Function(t) line.Contains(t.Key))

            If (Not String.IsNullOrWhitespace(transformation.Key)) Then

                strOutput.AppendLine(transformation.Value(line))

            Else

                strOutput.AppendLine(line)

            End If

        Next

        Console.WriteLine(strOutput)

    End Sub

​

End Module