File.ReadLines Method
Definition
Important
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Reads the lines of a file.
Overloads
| ReadLines(String, Encoding) |
Read the lines of a file that has a specified encoding. |
| ReadLines(String) |
Reads the lines of a file. |
ReadLines(String, Encoding)
- Source:
- File.cs
- Source:
- File.cs
- Source:
- File.cs
Read the lines of a file that has a specified encoding.
public:
static System::Collections::Generic::IEnumerable<System::String ^> ^ ReadLines(System::String ^ path, System::Text::Encoding ^ encoding);public static System.Collections.Generic.IEnumerable<string> ReadLines (string path, System.Text.Encoding encoding);static member ReadLines : string * System.Text.Encoding -> seq<string>Public Shared Function ReadLines (path As String, encoding As Encoding) As IEnumerable(Of String)Parameters
- path
- String
The file to read.
- encoding
- Encoding
The encoding that is applied to the contents of the file.
Returns
All the lines of the file, or the lines that are the result of a query.
Exceptions
.NET Framework and .NET Core versions older than 2.1: path is a zero-length string, contains only white space, or contains one or more invalid characters as defined by the GetInvalidPathChars() method.
path is null.
path is invalid (for example, it is on an unmapped drive).
The file specified by path was not found.
An I/O error occurred while opening the file.
path exceeds the system-defined maximum length.
The caller does not have the required permission.
path specifies a file that is read-only.
-or-
This operation is not supported on the current platform.
-or-
path is a directory.
-or-
The caller does not have the required permission.
Remarks
Use this method to specify an encoding to use read the file.
The ReadLines and ReadAllLines methods differ as follows: When you use ReadLines, you can start enumerating the collection of strings before the whole collection is returned. When you use ReadAllLines, you must wait for the whole array of strings be returned before you can access the array. Therefore, when you are working with very large files, ReadLines can be more efficient.
You can use the ReadLines method to do the following:
Perform LINQ to Objects queries on a file to obtain a filtered set of its lines.
Write the returned collection of lines to a file with the File.WriteAllLines(String, IEnumerable<String>, Encoding) method, or append them to an existing file with the File.AppendAllLines(String, IEnumerable<String>, Encoding) method.
Create an immediately populated instance of a collection that takes an IEnumerable<T> collection of strings for its constructor, such as a IList<T> or a Queue<T>.
Applies to
ReadLines(String)
- Source:
- File.cs
- Source:
- File.cs
- Source:
- File.cs
Reads the lines of a file.
public:
static System::Collections::Generic::IEnumerable<System::String ^> ^ ReadLines(System::String ^ path);public static System.Collections.Generic.IEnumerable<string> ReadLines (string path);static member ReadLines : string -> seq<string>Public Shared Function ReadLines (path As String) As IEnumerable(Of String)Parameters
- path
- String
The file to read.
Returns
All the lines of the file, or the lines that are the result of a query.
Exceptions
.NET Framework and .NET Core versions older than 2.1: path is a zero-length string, contains only white space, or contains one or more invalid characters defined by the GetInvalidPathChars() method.
path is null.
path is invalid (for example, it is on an unmapped drive).
The file specified by path was not found.
An I/O error occurred while opening the file.
path exceeds the system-defined maximum length.
The caller does not have the required permission.
path specifies a file that is read-only.
-or-
This operation is not supported on the current platform.
-or-
path is a directory.
-or-
The caller does not have the required permission.
Examples
The following example reads the lines of a file to find lines that contain specified strings.
foreach (string line in File.ReadLines(@"d:\data\episodes.txt"))
{
if (line.Contains("episode") & line.Contains("2006"))
{
Console.WriteLine(line);
}
}
for line in File.ReadLines @"d:\data\episodes.txt" do
if line.Contains "episode" && line.Contains "2006" then
printfn $"{line}"
For Each line As String In File.ReadLines("d:\data\episodes.txt")
If line.Contains("episode") And line.Contains("2006") Then
Console.WriteLine(line)
End If
Next line
The following example uses the ReadLines method in a LINQ query that enumerates all directories for files that have a .txt extension, reads each line of the file, and displays the line if it contains the string "Microsoft".
using System;
using System.IO;
using System.Linq;
class Program
{
static void Main(string[] args)
{
try
{
// Set a variable to the My Documents path.
string docPath =
Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
var files = from file in Directory.EnumerateFiles(docPath, "*.txt", SearchOption.AllDirectories)
from line in File.ReadLines(file)
where line.Contains("Microsoft")
select new
{
File = file,
Line = line
};
foreach (var f in files)
{
Console.WriteLine($"{f.File}\t{f.Line}");
}
Console.WriteLine($"{files.Count().ToString()} files found.");
}
catch (UnauthorizedAccessException uAEx)
{
Console.WriteLine(uAEx.Message);
}
catch (PathTooLongException pathEx)
{
Console.WriteLine(pathEx.Message);
}
}
}
open System
open System.IO
try
// Set a variable to the My Documents path.
let docPath =
Environment.GetFolderPath Environment.SpecialFolder.MyDocuments
let files =
query {
for file in Directory.EnumerateFiles(docPath, "*.txt", SearchOption.AllDirectories) do
for line in File.ReadLines file do
where (line.Contains "Microsoft")
select {| File = file; Line = line |}
}
for f in files do
printfn $"{f.File}\t{f.Line}"
printfn $"{Seq.length files} files found."
with
| :? UnauthorizedAccessException as uAEx -> printfn $"{uAEx.Message}"
| :? PathTooLongException as pathEx -> printfn $"{pathEx.Message}"
Imports System.IO
Imports System.Xml.Linq
Module Module1
Sub Main()
Try
Dim docPath As String = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments)
Dim files = From chkFile In Directory.EnumerateFiles(docPath, "*.txt", SearchOption.AllDirectories)
From line In File.ReadLines(chkFile)
Where line.Contains("Microsoft")
Select New With {.curFile = chkFile, .curLine = line}
For Each f In files
Console.WriteLine($"{f.File}\t{f.Line}")
Next
Console.WriteLine($"{files.Count} files found.")
Catch uAEx As UnauthorizedAccessException
Console.WriteLine(uAEx.Message)
Catch pathEx As PathTooLongException
Console.WriteLine(pathEx.Message)
End Try
End Sub
End Module
Remarks
The ReadLines and ReadAllLines methods differ as follows: When you use ReadLines, you can start enumerating the collection of strings before the whole collection is returned; when you use ReadAllLines, you must wait for the whole array of strings be returned before you can access the array. Therefore, when you are working with very large files, ReadLines can be more efficient.
You can use the ReadLines method to do the following:
Perform LINQ to Objects queries on a file to obtain a filtered set of its lines.
Write the returned collection of lines to a file with the File.WriteAllLines(String, IEnumerable<String>) method, or append them to an existing file with the File.AppendAllLines(String, IEnumerable<String>) method.
Create an immediately populated instance of a collection that takes an IEnumerable<T> collection of strings for its constructor, such as a IList<T> or a Queue<T>.
This method uses UTF8 for the encoding value.
