File.ReadLines(String) Method in C# with Examples

File.ReadLines(String) is an inbuilt File class method that is used to read the lines of a file.

Syntax:

public static System.Collections.Generic.IEnumerable ReadLines (string path);

Parameter: This function accepts a parameter which is illustrated below:

• path: This is the specified file for reading.

Exceptions:

• ArgumentException: The path is a zero-length string, contains only white space, or one or more invalid characters defined by the GetInvalidPathChars() method.
• ArgumentNullException: The path is null.
• DirectoryNotFoundException: The path is invalid.
• FileNotFoundException: The file specified by the path was not found.
• IOException: An I/O error occurred while opening the file.
• PathTooLongException: The path exceeds the system-defined maximum length.
• SecurityException: The caller does not have the required permission.
• UnauthorizedAccessException: The path specifies a file that is read-only. OR this operation is not supported on the current platform. OR the path is a directory. OR the caller does not have the required permission.

Return Value: Returns all the lines of the specified file.

Below are the programs to illustrate the File.ReadLines(String) method.

Program 1: Initially, a file file.txt is created with some contents shown below-

// C# program to illustrate the usage
// of File.ReadLines(String) method

// Using System and System.IO namespaces
using System;
using System.IO;

public class GFG {
    public static void Main(String[] argv)
    {
        // Calling the ReadLines(String) function
        foreach(string line in File.ReadLines(@"file.txt"))
        {
            // Printing the file contents
            Console.WriteLine(line);
        }
    }
}

Output:

GFG
gfg
Geeks
GeeksforGeeks
geeksforgeeks

Program 2: Initially, a file file.txt is created with some contents shown below-

Below code filter some contents from the file and prints them back.

// C# program to illustrate the usage
// of File.ReadLines(String) method

// Using System and System.IO namespaces
using System;
using System.IO;

public class GFG {
    public static void Main(String[] argv)
    {
        // Calling the ReadLines(String) function
        foreach(string line in File.ReadLines(@"file.txt"))
        {
            // Filtering the file contents and printing
            if (line.Contains("GFG")) {
                Console.WriteLine(line);
            }
        }
    }
}

Output:

GFG