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How to combine LINQ queries with regular expressions (Visual Basic)

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This example shows how to use the Regex class to create a regular expression for more complex matching in text strings. The LINQ query makes it easy to filter on exactly the files that you want to search with the regular expression, and to shape the results.

Example

Imports System.IO
Imports System.Text.RegularExpressions

Class LinqRegExVB

    Shared Sub Main()

        ' Root folder to query, along with all subfolders.
        ' Modify this path as necessary so that it accesses your Visual Studio folder.
        Dim startFolder As String = "C:\Program Files (x86)\Microsoft Visual Studio 14.0\"
        ' One of the following paths may be more appropriate on your computer.
        'Dim startFolder As String = "C:\Program Files (x86)\Microsoft Visual Studio\2017\"

        ' Take a snapshot of the file system.
        Dim fileList As IEnumerable(Of FileInfo) = GetFiles(startFolder)

        ' Create a regular expression to find all things "Visual".
        Dim searchTerm As New Regex("Visual (Basic|C#|C\+\+|Studio)")

        ' Search the contents of each .htm file.
        ' Remove the where clause to find even more matches!
        ' This query produces a list of files where a match
        ' was found, and a list of the matches in that file.
        ' Note: Explicit typing of "Match" in select clause.
        ' This is required because MatchCollection is not a
        ' generic IEnumerable collection.
        Dim queryMatchingFiles = From afile In fileList
                                Where afile.Extension = ".htm"
                                Let fileText = File.ReadAllText(afile.FullName)
                                Let matches = searchTerm.Matches(fileText)
                                Where (matches.Count > 0)
                                Select Name = afile.FullName,
                                       Matches = From match As Match In matches
                                                 Select match.Value

        ' Execute the query.
        Console.WriteLine("The term " & searchTerm.ToString() & " was found in:")

        For Each fileMatches In queryMatchingFiles
            ' Trim the path a bit, then write
            ' the file name in which a match was found.
            Dim s = fileMatches.Name.Substring(startFolder.Length - 1)
            Console.WriteLine(s)

            ' For this file, write out all the matching strings
            For Each match In fileMatches.Matches
                Console.WriteLine("  " + match)
            Next
        Next

        ' Keep the console window open in debug mode
        Console.WriteLine("Press any key to exit")
        Console.ReadKey()
    End Sub

    ' Function to retrieve a list of files. Note that this is a copy
    ' of the file information.
    Shared Function GetFiles(root As String) As IEnumerable(Of FileInfo)
        Return From file In My.Computer.FileSystem.GetFiles(
                   root, FileIO.SearchOption.SearchAllSubDirectories, "*.*")
               Select New FileInfo(file)
    End Function

End Class

Note that you can also query the MatchCollection object that is returned by a RegEx search. In this example only the value of each match is produced in the results. However, it is also possible to use LINQ to perform all kinds of filtering, sorting, and grouping on that collection. Because MatchCollection is a non-generic IEnumerable collection, you have to explicitly state the type of the range variable in the query.

Compile the code

Create a Visual Basic console application project, copy and paste the code sample, and adjust the Startup object value in the project properties.

See also