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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.

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();
    }
}

  • 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.

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

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