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How to: Query for Files with a Specified Attribute or Name

This example shows how to find all files that have a specified file name extension (for example ".txt") in a specified directory tree. It also shows how to return either the newest or oldest file in the tree based on the creation time.

Example

Module FindFileByExtension
    Sub Main()

        ' Change the drive\path if necessary
        Dim root As String = "C:\Program Files\Microsoft Visual Studio 9.0"

        'Take a snapshot of the folder contents
        Dim dir As New System.IO.DirectoryInfo(root)

        Dim fileList = dir.GetFiles("*.*", System.IO.SearchOption.AllDirectories)

        ' This query will produce the full path for all .txt files
        ' under the specified folder including subfolders.
        ' It orders the list according to the file name.
        Dim fileQuery = From file In fileList _
                        Where file.Extension = ".txt" _
                        Order By file.Name _
                        Select file

        For Each file In fileQuery
            Console.WriteLine(file.FullName)
        Next

        ' Create and execute a new query by using
        ' the previous query as a starting point.
        ' fileQuery is not executed again until the
        ' call to Last
        Dim fileQuery2 = From file In fileQuery _
                         Order By file.CreationTime _
                         Select file.Name, file.CreationTime

        ' Execute the query
        Dim newestFile = fileQuery2.Last

        Console.WriteLine("\r\nThe newest .txt file is {0}. Creation time: {1}", _
                newestFile.Name, newestFile.CreationTime)

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

    End Sub
End Module
class FindFileByExtension
{
    // This query will produce the full path for all .txt files
    // under the specified folder including subfolders.
    // It orders the list according to the file name.
    static void Main()
    {
        string startFolder = @"c:\program files\Microsoft Visual Studio 9.0\";

        // Take a snapshot of the file system.
        System.IO.DirectoryInfo dir = new System.IO.DirectoryInfo(startFolder);

        // This method assumes that the application has discovery permissions
        // for all folders under the specified path.
        IEnumerable<System.IO.FileInfo> fileList = dir.GetFiles("*.*", System.IO.SearchOption.AllDirectories);

        //Create the query
        IEnumerable<System.IO.FileInfo> fileQuery =
            from file in fileList
            where file.Extension == ".txt"
            orderby file.Name
            select file;

        //Execute the query. This might write out a lot of files!
        foreach (System.IO.FileInfo fi in fileQuery)
        {
            Console.WriteLine(fi.FullName);
        }

        // Create and execute a new query by using the previous 
        // query as a starting point. fileQuery is not 
        // executed again until the call to Last()
        var newestFile =
            (from file in fileQuery
             orderby file.CreationTime
             select new { file.FullName, file.CreationTime })
            .Last();

        Console.WriteLine("\r\nThe newest .txt file is {0}. Creation time: {1}",
            newestFile.FullName, newestFile.CreationTime);

        // Keep the console window open in debug mode.
        Console.WriteLine("Press any key to exit");
        Console.ReadKey();
    }
}

Compiling the Code

  • Create a Visual Studio project that targets the .NET Framework version 3.5. By default, the project has a reference to System.Core.dll and a using directive (C#) or Imports statement (Visual Basic) for the System.Linq namespace. In C# projects, add a using directive for the System.IO namespace.

  • Copy this code into your project.

  • Press F5 to compile and run the program.

  • Press any key to exit the console window.

Robust Programming

For intensive query operations over the contents of multiple types of documents and files, consider using the Windows Desktop Search engine.

See Also

Concepts

LINQ to Objects

LINQ and File Directories