How to: Query the Contents of Text Files in a Folder (LINQ) (C#)

This example shows how to query over all the files in a specified directory tree, open each file, and inspect its contents. This type of technique could be used to create indexes or reverse indexes of the contents of a directory tree. A simple string search is performed in this example. However, more complex types of pattern matching can be performed with a regular expression. For more information, see How to: Combine LINQ Queries with Regular Expressions (C#).


class QueryContents  
    public static void Main()  
        // Modify this path as necessary.  
        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);  
        string searchTerm = @"Visual Studio";  
        // Search the contents of each file.  
        // A regular expression created with the RegEx class  
        // could be used instead of the Contains method.  
        // queryMatchingFiles is an IEnumerable<string>.  
        var queryMatchingFiles =  
            from file in fileList  
            where file.Extension == ".htm"  
            let fileText = GetFileText(file.FullName)  
            where fileText.Contains(searchTerm)  
            select file.FullName;  
        // Execute the query.  
        Console.WriteLine("The term \"{0}\" was found in:", searchTerm);  
        foreach (string filename in queryMatchingFiles)  
        // Keep the console window open in debug mode.  
        Console.WriteLine("Press any key to exit");  
    // Read the contents of the file.  
    static string GetFileText(string name)  
        string fileContents = String.Empty;  
        // If the file has been deleted since we took   
        // the snapshot, ignore it and return the empty string.  
        if (System.IO.File.Exists(name))  
            fileContents = System.IO.File.ReadAllText(name);  
        return fileContents;  

Compiling the Code

Create a C# console application project, with using directives for the System.Linq and System.IO namespaces.

See also