Read entire file

Read entire file
You are encouraged to solve this task according to the task description, using any language you may know.

Load the entire contents of some text file as a single string variable.

If applicable, discuss: encoding selection, the possibility of memory-mapping.

Of course, one should avoid reading an entire file at once if the file is large and the task can be accomplished incrementally instead (in which case check File IO); this is for those cases where having the entire file is actually what is wanted.

Ada

Ada.Direct_IO

Works with: Ada 2005

Using Ada.Directories to first ask for the file size and then Ada.Direct_IO to read the whole file in one chunk:

with Ada.Directories,
     Ada.Direct_IO,
     Ada.Text_IO;
 
procedure Whole_File is
 
   File_Name : String  := "whole_file.adb";
   File_Size : Natural := Natural (Ada.Directories.Size (File_Name));
 
   subtype File_String    is String (1 .. File_Size);
   package File_String_IO is new Ada.Direct_IO (File_String);
 
   File     : File_String_IO.File_Type;
   Contents : File_String;
 
begin
   File_String_IO.Open  (File, Mode => File_String_IO.In_File,
                               Name => File_Name);
   File_String_IO.Read  (File, Item => Contents);
   File_String_IO.Close (File);
 
   Ada.Text_IO.Put (Contents);
end Whole_File;

This kind of solution is limited a bit by the fact that the GNAT implementation of Ada.Direct_IO first allocates a copy of the read object on the stack inside Ada.Direct_IO.Read. On Linux you can use the command "limit stacksize 1024M" to increase the available stack for your processes to 1Gb, which gives your program more freedom to use the stack for allocating objects.

POSIX.Memory_Mapping

Works with: POSIX

Works with: Ada 95

Mapping the whole file into the address space of your process and then overlaying the file with a String object.

with Ada.Text_IO,
     POSIX.IO,
     POSIX.Memory_Mapping,
     System.Storage_Elements;
 
procedure Read_Entire_File is
 
   use POSIX, POSIX.IO, POSIX.Memory_Mapping;
   use System.Storage_Elements;
 
   Text_File    : File_Descriptor;
   Text_Size    : System.Storage_Elements.Storage_Offset;
   Text_Address : System.Address;
 
begin
   Text_File := Open (Name => "read_entire_file.adb",
                      Mode => Read_Only);
   Text_Size := Storage_Offset (File_Size (Text_File));
   Text_Address := Map_Memory (Length     => Text_Size,
                               Protection => Allow_Read,
                               Mapping    => Map_Shared,
                               File       => Text_File,
                               Offset     => 0);
 
   declare
      Text : String (1 .. Natural (Text_Size));
      for Text'Address use Text_Address;
   begin
      Ada.Text_IO.Put (Text);
   end;
 
   Unmap_Memory (First  => Text_Address,
                 Length => Text_Size);
   Close (File => Text_File);
end Read_Entire_File;

Character encodings and their handling are not really specified in Ada. What Ada does specify is three different character types (and corresponding string types):

• Character - containing the set of ISO-8859-1 characters.
• Wide_Character - containing the set of ISO-10646 BMP characters.
• Wide_Wide_Character - containing the full set of ISO-10646 characters.

The GNU Ada compiler (GNAT) seems to read in text files as bytes, completely ignoring any operating system information on character encoding. You can use -gnatW8 in Ada 2005 mode to use UTF-8 characters in identifier names.

AutoHotkey

 
fileread, varname, C:\filename.txt ; adding "MsgBox %varname%" (no quotes) to the next line will display the file contents.

This script works fine as-is provided C:\filename.txt exists.

ALGOL 68

In official ALGOL 68 a file is composed of pages, lines and characters, however for ALGOL 68 Genie and ELLA ALGOL 68RS this concept is not supported as they adopt the Unix concept of files being "flat", and hence contain only characters.

The book can contain new pages and new lines, are not of any particular character set, hence are system independent. The character set is set by a call to make conv, eg make conv(tape, ebcdic conv); - c.f. Character_codes for more details.

In official/standard ALGOL 68 only:

MODE BOOK = FLEX[0]FLEX[0]FLEX[0]CHAR; ¢ pages of lines of characters ¢
BOOK book;
 
FILE book file;
INT errno = open(book file, "book.txt", stand in channel);
 
get(book file, book)

Once a "book" has been read into a book array it can still be associated with a virtual file and again be accessed with standard file routines (such as readf, printf, putf, getf, new line etc). This means data can be directly manipulated from a array cached in "core" using transput (stdio) routines.

In official/standard ALGOL 68 only:

FILE cached book file;
associate(cached book file, book)

AWK

#!/usr/bin/awk -f
BEGIN { 
   ## empty record separate, 
   RS="";
   ## read line (i.e. whole file) into $0	
   getline; 	
   ## print line number and content of line 
   print "=== line "NR,":",$0; 
}
{
   ## no further line is read printed 
   print "=== line "NR,":",$0; 
}

BASIC

Whether or not various encodings are supported is implementation-specific.

Works with: QBasic

DIM f AS STRING
OPEN "file.txt" FOR BINARY AS 1
f = SPACE$(LOF(1))
GET #1, 1, f
CLOSE 1

BBC BASIC

In BBC BASIC for Windows and Brandy BASIC the maximum string length is 65535 characters.

      file% = OPENIN("input.txt")
      strvar$ = ""
      WHILE NOT EOF#file%
        strvar$ += CHR$(BGET#file%)
      ENDWHILE
      CLOSE #file%

API version:

Works with: BBC BASIC for Windows

      file% = OPENIN("input.txt")
      strvar$ = STRING$(EXT#file%, " ")
      SYS "ReadFile", @hfile%(file%), !^strvar$, EXT#file%, ^temp%, 0
      CLOSE #file%

Bracmat

get'(filename,STR):?myString

Brainf***

While the language certainly doesn't support strings in the traditional sense, relaxing the definition to mean any contiguous sequence of null-terminated bytes permits a reasonable facsimile. This cat program eschews the simpler byte-by-byte approach (,[.,]) to demonstrate the technique.

>     Keep cell 0 at 0 as a sentinel value
,[>,] Read into successive cells until EOF
<[<]  Go all the way back to the beginning
>[.>] Print successive cells while nonzero

Output:

$ curl -Ls rosettacode.org | bf ">,[>,]<[<]>[.>]"
<!DOCTYPE html>
...
</html>
Tape: [0, 60, 33, 68, 79, 67, 84, 89, 80, 69, 32, 104, 116, 109, 108, 62, 10 ... 60, 47, 104, 116, 109, 108, 62, 10, 0]

Brat

include :file
 
file.read file_name

C

It is not possible to specify encodings: the file is read as binary data (on some system, the b flag is ignored and there's no difference between "r" and "rb"; on others, it changes the way the "new lines" are treated, but this should not affect fread)

#include <stdio.h>
#include <stdlib.h>
 
int main()
{
  char *buffer;
  FILE *fh = fopen("readentirefile.c", "rb");
  if ( fh != NULL )
  {
    fseek(fh, 0L, SEEK_END);
    long s = ftell(fh);
    rewind(fh);
    buffer = malloc(s);
    if ( buffer != NULL )
    {
      fread(buffer, s, 1, fh);
      // we can now close the file
      fclose(fh); fh = NULL;
 
      // do something, e.g.
      fwrite(buffer, s, 1, stdout);
 
      free(buffer);
    }
    if (fh != NULL) fclose(fh);
  }
  return EXIT_SUCCESS;
}

Works with: POSIX

We can memory-map the file.

#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>
 
int main()
{
  char *buffer;
  struct stat s;
 
  int fd = open("readentirefile_mm.c", O_RDONLY);
  if (fd < 0 ) return EXIT_FAILURE;
  fstat(fd, &s);
  /* PROT_READ disallows writing to buffer: will segv */
  buffer = mmap(0, s.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
 
  if ( buffer != (void*)-1 )
  {
    /* do something */
    fwrite(buffer, s.st_size, 1, stdout);
    munmap(buffer, s.st_size);
  }
 
  close(fd);
  return EXIT_SUCCESS;
}

C++

#include <iostream>
#include <fstream>
#include <string>
#include <iterator>
 
int main( ) {
   std::ifstream infile( "sample.txt" ) ;
   if ( infile ) {
      std::string fileData( ( std::istreambuf_iterator<char> ( infile ) ) ,
	    std::istreambuf_iterator<char> ( ) ) ;
      infile.close( ) ; ;
      return 0 ;
   }
   else {
      std::cout << "file not found!\n" ;
      return 1 ;
   }
}
 

C#

Works with: C sharp version 3.0

using System.IO;
 
class Program
{
    static void Main(string[] args)
    {
        var fileContents = File.ReadAllText("c:\\autoexec.bat");
    }
}
 

Clojure

The core function slurp does the trick; you can specify an encoding as an optional second argument:

(slurp "myfile.txt")
(slurp "my-utf8-file.txt" "UTF-8")

CMake

Sets a variable named string.

file(READ /etc/passwd string)

This works with text files, but fails with binary files that contain NUL characters. CMake truncates the string at the first NUL character, and there is no way to detect this truncation.

The only way to read binary files is to use the HEX keyword to convert the entire file to a hexadecimal string.

file(READ /etc/pwd.db string HEX)

Common Lisp

(defun file-string (path)
  (with-open-file (stream path)
    (let ((data (make-string (file-length stream))))
      (read-sequence data stream)
      data)))

D

import std.file: read, readText;
 
void main() {
    // To read a whole file into a dynamic array of unsigned bytes:
    auto data = cast(ubyte[])read("unixdict.txt");
 
    // To read a whole file into a validated UTF-8 string:
    string txt = readText("unixdict.txt");
}

Delphi

Using TStringList

program ReadAll;
 
{$APPTYPE CONSOLE}
 
uses Classes;
 
var
  i: Integer;
  lList: TStringList;
begin
  lList := TStringList.Create;
  try
    lList.LoadFromFile('c:\input.txt');
    // Write everything at once
    Writeln(lList.Text);
    // Write one line at a time
    for i := 0 to lList.Count - 1 do
      Writeln(lList[i]);
  finally
    lList.Free;
  end;
end.

Works with: Delphi 2010 and above

program ReadAll;
 
{$APPTYPE CONSOLE}
 
uses
  SysUtils, IOUtils;
 
begin
// with default encoding:
  Writeln(TFile.ReadAllText('C:\autoexec.bat'));
// with encoding specified:
  Writeln(TFile.ReadAllText('C:\autoexec.bat', TEncoding.ASCII));
  Readln;
end.

E

<file:foo.txt>.getText()

The file is assumed to be in the default encoding.

Erlang

{ok, B} = file:read_file("myfile.txt").

This reads the entire file into a binary object.

Euphoria

Euphoria cannot natively handle multibyte character encodings. The openEuphoria team is/was working on supporting it. It may have been implemented by now.

 
function load_file(sequence filename)
  integer fn,c
  sequence data
    fn = open(filename,"r") -- "r" for text files, "rb" for binary files
    if (fn = -1) then return {} end if -- failed to open the file
 
    data = {} -- init to empty sequence
    c = getc(fn) -- prime the char buffer
    while (c != -1) do -- while not EOF
      data &= c -- append each character
      c = getc(fn) -- next char
    end while
 
    close(fn)
    return data
end function
 

F#

// read entire file into variable using default system encoding or with specified encoding
open System.IO
let data = File.ReadAllText(filename)
let utf8 = File.ReadAllText(filename, System.Text.Encoding.UTF8)

Factor

USING: io.encodings.ascii io.encodings.binary io.files ;
 
! to read entire file as binary
"foo.txt" binary file-contents
 
! to read entire file as lines of text
"foo.txt" ascii file-lines

Fantom

Provide the filename to read from as a command-line parameter.

 
class ReadString
{
  public static Void main (Str[] args)
  {
    Str contents := File(args[0].toUri).readAllStr
    echo ("contents: $contents")
  }
}
 

Forth

Works with: GNU Forth

s" foo.txt" slurp-file   ( str len )

Frink

The read[URL] function reads the entire contents of a URL. The encoding can be specified if necessary.

 
a = read["file:yourfile.txt"]
b = read["file:yourfile.txt", "UTF-8"]
 

GAP

InputTextFile("input.txt");
s := ReadAll(f);;  # two semicolons to hide the result, which may be long
CloseStream(f);

Go

Go has good support for working with strings as UTF-8, but there is no requirement that strings be UTF-8 and in fact they can hold arbitrary data. ioutil.ReadFile returns the contents of the file unaltered as a byte array. The conversion in the next line from byte array to string also makes no changes to the data. In the example below sv will have an exact copy of the data in the file, without regard to encoding.

import "io/ioutil"
 
data, err := ioutil.ReadFile(filename)
sv := string(data)

Go also supports memory mapped files through Linux mmap. The following prints the contents of "file".

package main
 
import (
    "fmt"
    "log"
    "os"
    "syscall"
)
 
func main() {
    f, err := os.Open("file")
    if err != nil {
        log.Fatal(err)
    }
    fi, err := f.Stat()
    if err != nil {
        log.Fatal(err)
    }
    data, err := syscall.Mmap(int(f.Fd()), 0, int(fi.Size()),
        syscall.PROT_READ, syscall.MAP_PRIVATE)
    if err != nil {
        log.Fatal(err)
    }
    fmt.Println(string(data))
}

Groovy

def fileContent = new File("c:\\file.txt").text

GUISS

Start,Programs,Accessories,Notepad,Menu:File,Open,Doubleclick:Icon:Notes.TXT,Button:OK

Haskell

In the IO monad:

do text <- readFile filepath
   -- do stuff with text

Note that readFile is lazy. If you want to ensure the entire file is read in at once, before any other IO actions are run, try:

eagerReadFile :: FilePath -> IO String
eagerReadFile filepath = do
    text <- readFile filepath
    last text `seq` return text

Icon and Unicon

The first code snippet below reads from stdin directly into the string fs, preserving line separators (if any) and reading in large chunks.

every (fs := "") ||:= |reads(1000000)

The second code snippet below performs the same operation using an intermediate list fL and applying a function (e.g. FUNC) to each line. Use this form when you need to perform additional string functions such as 'trim' or 'map' on each line. This avoids unnecessary garbage collections which will occur with larger files. The list can be discarded when done. Line separators are mapped into newlines.

every put(fL := [],|FUNC(read()))
every (fs := "") ||:= !fL || "\n"
fL := &null

Inform 7

File access is sandboxed by the interpreter, so this solution essentially requires that the file have been previously written by an Inform program running from the same location under the same interpreter.

Works with: Glulx virtual machine

Home is a room.
 
The File of Testing is called "test".
 
When play begins:
	say "[text of the File of Testing]";
	end the story.

J

   var=: 1!:1<'foo.txt'

To memory map the file:

   require'jmf'
   JCHAR map_jmf_ 'var';'foo.txt'

Caution: updating the value of the memory mapped variable will update the file, and this characteristic remains when the variable's value is passed, unmodified, to a verb which modifies its own local variables.

Java

There is no single method to do this in Java 6 and below (probably because reading an entire file at once could fill up your memory quickly), so to do this you could simply append the contents as you read them into a buffer.

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
 
public class ReadFile {
    public static void main(String[] args) throws IOException{
        String fileContents = readEntireFile("./foo.txt");
    }
 
    private static String readEntireFile(String filename) throws IOException {
        FileReader in = new FileReader(filename);
        StringBuilder contents = new StringBuilder();
        char[] buffer = new char[4096];
        int read = 0;
        do {
            contents.append(buffer, 0, read);
            read = in.read(buffer);
        } while (read >= 0);
        return contents.toString();
    }
}

One can memory-map the file in Java, but there's little to gain if one is to create a String out of the file:

 
import java.nio.channels.FileChannel.MapMode;
import java.nio.MappedByteBuffer;
import java.io.RandomAccessFile;
import java.io.IOException;
import java.io.File;
 
public class MMapReadFile {
	public static void main(String[] args) throws IOException {
		MappedByteBuffer buff = getBufferFor(new File(args[0]));
                String results = new String(buff.asCharBuffer());
	}
 
	public static MappedByteBuffer getBufferFor(File f) throws IOException {  
		RandomAccessFile file = new RandomAccessFile(f, "r");
 
		MappedByteBuffer buffer = file.getChannel().map(MapMode.READ_ONLY, 0, f.length());
		file.close();
		return buffer;
	}
}

or one can take a shortcut:

String content = new Scanner(new File("foo"), "UTF-8").useDelimiter("\\A").next();

this works because Scanner will search the file for a delimiter and return everything before that. \A is the beginning of the file, which it will never find until the end of the file is reached.

Works with: Java version 7+

Java 7 added java.nio.file.Files which has two methods for accomplishing this task: Files.readAllLines and Files.readAllBytes:

import java.util.List;
import java.nio.charset.Charset;
import java.nio.file.*;
 
public class ReadAll {
	public static List<String> readAllLines(String filesname){
		Path file = Paths.get(filename);
		return Files.readAllLines(file, Charset.defaultCharset());
	}
 
	public static byte[] readAllBytes(String filename){
		Path file = Paths.get(filename);
		return Files.readAllBytes(file);
	}
}

JavaScript

This works in IExplorer or a standalone js file. Note the similarity to the VBScript code.

var fso=new ActiveXObject("Scripting.FileSystemObject");
var f=fso.OpenTextFile("c:\\myfile.txt",1);
var s=f.ReadAll();
f.Close();
try{alert(s)}catch(e){WScript.Echo(s)}

The following works in all browsers, including IE10.

var file = document.getElementById("fileInput").files.item(0); //a file input element
if (file) {
	var reader = new FileReader();
	reader.readAsText(file, "UTF-8");
	reader.onload = loadedFile;
	reader.onerror = errorHandler;
}
function loadedFile(event) {
	var fileString = event.target.result;
	alert(fileString);
}
function errorHandler(event) {
	alert(event);
}
 

Julia

 
sample_filepath = "/devel/myfile.txt"
f = open(sample_filepath)
file_contents = readall(f)    # load all into a single String
close(f)
 

LabVIEW

This image is a VI Snippet, an executable image of LabVIEW code. The LabVIEW version is shown on the top-right hand corner. You can download it, then drag-and-drop it onto the LabVIEW block diagram from a file browser, and it will appear as runnable, editable code.

Lang5

'foo.txt slurp

Liberty BASIC

filedialog "Open a Text File","*.txt",file$
if file$<>"" then
    open file$ for input as #1
    entire$ = input$(#1, lof(#1))
    close #1
    print entire$
end if

Lua

 
--If the file opens with no problems, io.open will return a
--handle to the file with methods attached.
--If the file does not exist, io.open will return nil and
--an error message.
--assert will return the handle to the file if present, or
--it will throw an error with the message returned second
--by io.open.
local file = assert(io.open(filename))
--Without wrapping io.open in an assert, local file would be nil,
--which would cause an 'attempt to index a nil value' error when
--calling file:read.
 
--file:read takes the number of bytes to read, or a string for
--special cases, such as "*a" to read the entire file.
local contents = file:read'*a'
 
--If the file handle was local to the expression
--(ie. "assert(io.open(filename)):read'a'"),
--the file would remain open until its handle was
--garbage collected.
file:close()
 

Maple

First solution:

 
s1 := readbytes( "file1.txt", infinity, TEXT ):
 

Second solution:

 
s2 := FileTools:-Text:-ReadFile( "file2.txt" ):
 

Mathematica

Import["filename","String"]

MATLAB / Octave

  fid = fopen('filename','r');
  [str,count] = fread(fid, [1,inf], 'uint8=>char');  % s will be a character array, count has the number of bytes
  fclose(fid); 

Mercury

:- module read_entire_file.
:- interface.
 
:- import_module io.
:- pred main(io::di, io::uo) is det.
 
:- implementation.
:- import_module string.
 
main(!IO) :-
   io.open_input("file.txt", OpenResult, !IO),
   (
      OpenResult = ok(File),
      io.read_file_as_string(File, ReadResult, !IO),
      (
           ReadResult = ok(FileContents),
           io.write_string(FileContents, !IO)
      ;
           ReadResult = error(_, IO_Error),
           io.stderr_stream(Stderr, !IO),
           io.write_string(Stderr, io.error_message(IO_Error) ++ "\n", !IO)
      )        
   ;
      OpenResult = error(IO_Error),
      io.stderr_stream(Stderr, !IO),
      io.write_string(Stderr, io.error_message(IO_Error) ++ "\n", !IO)
   ).

NetRexx

/* NetRexx */
options replace format comments java crossref symbols nobinary
 
parse arg inFileName .
 
if inFileName = '' | inFileName = '.' then inFileName = './data/dwarfs.json'
fileContents = slurp(inFileName)
say fileContents
 
return
 
-- Slurp a file and return contents as a Rexx string
method slurp(inFileName) public static returns Rexx
 
  slurped = Rexx null
  slurpStr = StringBuilder()
  ioBuffer = byte[1024]
  inBytes = int 0
 
  do
    inFile = File(inFileName)
    inFileIS = BufferedInputStream(FileInputStream(inFile))
 
    loop label ioLoop until inBytes = -1
      slurpStr.append(String(ioBuffer, 0, inBytes))
      inBytes = inFileIS.read(ioBuffer)
      end ioLoop
 
  catch exFNF = FileNotFoundException
    exFNF.printStackTrace
  catch exIO = IOException
    exIO.printStackTrace
  finally
    do
      inFileIS.close()
    catch ex = IOException
      ex.printStackTrace
    end
  end
 
  slurped = Rexx(slurpStr.toString)
 
  return slurped
 

NewLISP

(read-file "filename")

Nimrod

readFile(filename)

Objeck

 
string := FileReader->ReadFile("in.txt");
 

Objective-C

 
    /*** 0. PREPARATION    */
    // We need a text file to read; let's redirect a C string to a new file
    // using the shell by way of the stdlib system() function.
    system ("echo \"Hello, World!\" > ~/HelloRosetta");
 
 
 
    /*** 1. THE TASK      */
    // Instantiate an NSString which describes the filesystem location of
    // the file we will be reading.
    NSString *filePath = [NSHomeDirectory() stringByAppendingPathComponent:@"HelloRosetta"];
 
    // The selector we're going to use to complete this task,
    // stringWithContentsOfFile:encoding:error, has an optional `error'
    // parameter which can be used to return information about any
    // errors it might run into. It's optional, but we'll create an NSError
    // anyways to demonstrate best practice.
    NSError *anError;
 
    // And finally, the task: read and store the contents of a file as an
    // NSString.
    NSString *aString = [NSString stringWithContentsOfFile:filePath
                                                  encoding:NSUTF8StringEncoding
                                                     error:&anError];
 
    // If the file read was unsuccessful, display the error description.
    // Otherwise, display the NSString.
    if (!aString) {
        NSLog(@"%@", [anError localizedDescription]);
    } else {
        NSLog(@"%@", aString);
    }
 

OCaml

For most uses we can use this function:

let load_file f =
  let ic = open_in f in
  let n = in_channel_length ic in
  let s = String.create n in
  really_input ic s 0 n;
  close_in ic;
  (s)

There is no problem reading an entire file with the function really_input because this function is implemented appropriately with an internal loop, but it can only load files which size is equal or inferior to the maximum length of an ocaml string. This maximum size is available with the variable Sys.max_string_length. On 32 bit machines this size is about 16Mo.

To load bigger files several solutions exist, for example create a structure that contains several strings where the contents of the file can be split. Or another solution that is often used is to use a bigarray of chars instead of a string:

type big_string =
  (char, Bigarray.int8_unsigned_elt, Bigarray.c_layout) Bigarray.Array1.t

The function below returns the contents of a file with this type big_string, and it does so with "memory-mapping":

let load_big_file filename =
  let fd = Unix.openfile filename [Unix.O_RDONLY] 0o640 in
  let len = Unix.lseek fd 0 Unix.SEEK_END in
  let _ = Unix.lseek fd 0 Unix.SEEK_SET in
  let shared = false in  (* modifications are done in memory only *)
  let bstr = Bigarray.Array1.map_file fd
               Bigarray.char Bigarray.c_layout shared len in
  Unix.close fd;
  (bstr)

Then the length of the data can be get with Bigarray.Array1.dim instead of String.length, and we can access to a given char with the syntactic sugar bstr.{i} (instead of str.[i]) as shown in the small piece of code below (similar to the cat command):

let () =
  let bstr = load_big_file Sys.argv.(1) in
  let len = Bigarray.Array1.dim bstr in
  for i = 0 to pred len do
    let c = bstr.{i} in
    print_char c
  done

ooRexx

 
file = 'c:\test.txt'
myStream = .stream~new(file)
myString = myStream~charIn(,myStream~chars)
 

Streams are opened on demand and closed when the script finishes. It is possible if you wish to open and close the streams explicitly

 
file = 'c:\test.txt'
myStream = .stream~new(file)
if mystream~open('read') = 'READY:'
then do
   myString = myStream~charIn(,myStream~chars)
   myStream~close
end
 

OxygenBasic

Two Formats:

string s

'AS FUNCTION

s=GetFile "t.txt"

'AS PROCEDURE

Getfile "t.txt",s

Oz

The interface for file operations is object-oriented.

declare
  FileHandle = {New Open.file init(name:"test.txt")}
  FileContents = {FileHandle read(size:all list:$)}
in
  {FileHandle close}
  {System.printInfo FileContents}

FileContents is a list of bytes. The operation does not assume any particular encoding.

PARI/GP

GP's ability to read files is extremely limited; reading an entire file is almost all that it can do. PARI is not similarly limited.

text=read("file.txt");

Pascal

See TStrignList example of Delphi

Perl

open my $fh, $filename;
my $text = do { local( $/ ); <$fh> };
close $fh;

or

open my $fh, $filename;
my $text;read $fh, $text, -s $filename;
close $fh;

or

use File::Slurp;
my $text = read_file($filename);

or the IO::All module provides several ways:

use IO::All;
$text = io($filename)->all;
$text = io($filename)->utf8->all;
@text = io($filename)->slurp;
$text < io($filename);
io($filename) > $text;

For a one-liner from shell, use -0[code]. It normally specifies the oct char code of record separator ($/), so for example perl -n -040 would read chunks of text ending at each space ($/ = ' '). However, -0777 has special meaning: $/ = undef, so the whole file is read in at once (chr 0777 happens to be "ǿ", but Larry doesn't think one should use that as record separator).

perl -n -0777 -e 'print "file len: ".length' stuff.txt

Perl 6

Works with: Rakudo version 2010.07

my $string = slurp 'sample.txt';

PHP

file_get_contents($filename)

PicoLisp

Using 'till' is the shortest way:

(in "file" (till NIL T))

To read the file into a list of characters:

(in "file" (till NIL))

or, more explicit:

(in "file" (make (while (char) (link @))))

Encoding is always assumed to be UTF-8.

Pike

string content=Stdio.File("foo.txt")->read();

PL/I

 
get file (in) edit ((substr(s, i, 1) do i = 1 to 32767)) (a);
 

PowerShell

Get-Content foo.txt

This will only detect Unicode correctly with a BOM in place (even for UTF-8). With explicit selection of encoding:

Get-Content foo.txt -Encoding UTF8

However, both return an array of strings which is fine for pipeline use but if a single string is desired the array needs to be joined:

(Get-Content foo.txt) -join "`n"

PureBasic

A file can be read with any of the built in commands

Number.b = ReadByte(#File)
Length.i = ReadData(#File, *MemoryBuffer, LengthToRead)
Number.c = ReadCharacter(#File)
Number.d = ReadDouble(#File)
Number.f = ReadFloat(#File)
Number.i = ReadInteger(#File)
Number.l = ReadLong(#File)
Number.q = ReadQuad(#File)
Text$    = ReadString(#File [, Flags])
Number.w = ReadWord(#File)

If the file is s pure text file (no CR/LF etc.), this will work and will read each line untill EOL is found.

If ReadFile(0, "RC.txt")       
  Variable$=ReadString(0)     
  CloseFile(0) 
EndIf

Since PureBasic terminates strings with a #NULL and also split the ReadString() is encountering new line chars, any file containing these must be treated as a data stream.

Title$="Select a file"
Pattern$="Text (.txt)|*.txt|All files (*.*)|*.*"
fileName$ = OpenFileRequester(Title$,"",Pattern$,0)
If fileName$
  If ReadFile(0, fileName$)
    length = Lof(0)     
    *MemoryID = AllocateMemory(length)  
    If *MemoryID
      bytes = ReadData(0, *MemoryID, length)
      MessageRequester("Info",Str(bytes)+" was read")
    EndIf
    CloseFile(0)
  EndIf
EndIf

Python

open(filename).read()

This returns a byte string and does not assume any particular encoding.

In Python 3 strings are in unicode, you can specify encoding when reading:

open(filename, encoding='utf-8').read()

R

fname <- "notes.txt"
contents <- readChar(fname, file.info(fname)$size)

Racket

(file->string "foo.txt")

Raven

'myfile.txt' read as $content_as_string

or

'file://r:/home/me/myfile.txt' open as $handle
$handle read as $content_as_string
$handle close

REALbasic

This function accepts a file (FolderItem object) and an optional TextEncoding class. If the TextEncoding is not defined, then REALbasic defaults to UTF-8. Since it is intended for cross-platform development, REALbasic has a number of built-in tools for working with different text encodings, line terminators, etc. [1]

 
Function readFile(theFile As FolderItem, txtEncode As TextEncoding = Nil) As String
  Dim fileContents As String
  Dim tis As TextInputStream
  tis = tis.Open(theFile)
  fileContents = tis.ReadAll(txtEncode)
  tis.Close
  Return fileContents
 
Exception err As NilObjectException
  MsgBox("File Not Found.")
End Function
 

REBOL

read %my-file  ; read as text
read/binary %my-file       ; preserve contents exactly

Retro

with files'
here "input.txt" slurp

REXX

/*REXX program to read a file and store it as a continuous char string. */
 
iFID = 'a_file'                        /*name of the input file.        */
aString = 
 
  do  while lines(iFID)\==0            /*read until finished.           */
  aString = aString || linein(iFID)    /*append input to  Astring.      */
  end   /*while*/
                                       /*stick a fork in it, we're done.*/

Ruby

IO.read is for text files. It uses the default text encodings, and on Microsoft Windows, it also converts "\r\n" to "\n".

# Read entire text file.
str = IO.read "foobar.txt"
 
# It can also read a subprocess.
str = IO.read "| grep ftp /etc/services"

Caution! IO.read and File.read take a portname. To open an arbitrary path (which might start with "|"), you must use File.open, then IO#read.

path = "|strange-name.txt"
str = File.open(path) {|f| f.read}

To read a binary file, open it in binary mode.

# Read entire binary file.
str = File.open(path, "rb") {|f| f.read}

Ruby 1.9 can read text files in different encodings.

Works with: Ruby version 1.9

# Read EUC-JP text from file.
str = File.open(path, "r:euc-jp") {|f| f.read}
 
# Read EUC-JP text from file; transcode text from EUC-JP to UTF-8.
str = File.open(path, "r:euc-jp:utf-8") {|f| f.read}

Seed7

The library getf.s7i defines the function getf, which reads a whole file into a string:

$ include "seed7_05.s7i";
  include "getf.s7i";

const proc: main is func
  local
    var string: fileContent is "";
  begin
    fileContent := getf("text.txt");
  end func;

Smalltalk

Works with: Pharo

(StandardFileStream oldFileNamed: 'foo.txt') contents

Works with: Smalltalk/X

'foo.txt' asFilename contentsAsString

SNOBOL4

In SNOBOL4, file I/O is done by associating a variable with the desired file, via the input() built-in function. After the association, each reference to the named variable provides as the variable's value the next block or line of data from the corresponding file. The exact format of the input() function parameters tends to vary based on the implementation in use. In this example, the code reads the file in blocks of 512k bytes (or less) until the entire file has been read into one long string in memory.

      input(.inbin,21,"filename.txt [-r524288]")     :f(end)
rdlp  buf = inbin                                    :s(rdlp)
*
*  now process the 'buf' containing the file
*
end

Tcl

This reads the data in as text, applying the default encoding translations.

set f [open $filename]
set data [read $f]
close $f

To read the data in as uninterpreted bytes, either use fconfigure to put the handle into binary mode before reading, or (from Tcl 8.5 onwards) do this:

set f [open $filename "rb"]
set data [read $f]
close $f

TUSCRIPT

 
$$ MODE TUSCRIPT
ERROR/STOP OPEN ("rosetta.txt",READ,-std-)
var=FILE ("rosetta.txt")
 

TXR

@(next "foo.txt")
@(freeform)
@LINE
 

The freeform directive in TXR causes the remaining lines of the text stream to be treated as one big line, catenated together. The default line terminator is the newline "\n". This lets the entire input be captured into a single variable as a whole-line match.

UNIX Shell

We start a 'cat' process to read the entire file, and use '$(...)' to grab the output of 'cat'. We use 'printf' which might be more portable than 'echo'. Because '$(...)' can chop off a newline at the end of the file, we tell 'printf' to add an extra newline.

f=`cat foo.txt`    # f will contain the entire contents of the file
printf '%s\n' "$f"

f=$(cat foo.txt)
printf '%s\n' "$f"

Some shells provide a shortcut to read a file without starting a 'cat' process.

Works with: bash

Works with: pdksh

f=$(<foo.txt)
echo -E "$f"

Works with: zsh

file=$(<foo.txt)
print $file

alternatively

zmodload zsh/mapfile
print $mapfile[foo.txt]

Vala

 
string file_contents;
FileUtils.get_contents("foo.txt", out file_contents);
 

VBScript

Read text file with default encoding into variable and display

dim s
s = createobject("scripting.filesystemobject").opentextfile("slurp.vbs",1).readall
wscript.echo s

Read text file with UTF-16 encoding into memory and display

wscript.echo createobject("scripting.filesystemobject").opentextfile("utf16encoded.txt",1,-1).readall

Vedit macro language

In Vedit Macro Language, a "string variable" can be either an edit buffer or a text register.
Text registers can hold only a limited amount of data (about 120 KB each in current version).
Edit buffers can handle files of unlimited size (even larger than the size of virtual memory). For large files, only a part of the file is kept in memory, but from users point of view there is no practical difference to having the whole file in memory.

Read file into edit buffer. The buffer is allocated automatically:

File_Open("example.txt")

Read file into text register 10:

Reg_Load(10, "example.txt")

Visual Basic .NET

Imports System.IO
 
Public Class Form1
 
  ' Read all of the lines of a file.
  ' Function assumes that the file exists.
  Private Sub ReadLines(ByVal FileName As String)
 
    Dim oReader As New StreamReader(FileName)
    Dim sLine As String = oReader.ReadToEnd()
 
    oReader.Close()
 
  End Sub
 
End Class

XPL0

This example reads its own source code file and displays it as a string. The command line is: readfile <readfile.xpl

include c:\cxpl\codes;  \intrinsic 'code' declarations
string 0;               \use zero-terminated string convention
int  I;
char Str;
[Str:= GetHp;           \starting address of block of local "heap" memory
I:= 0;                  \ [does the exact same thing as Reserve(0)]
loop    [Str(I):= ChIn(1);
        if Str(I) = $1A\EOF\ then [Str(I):= 0;  quit];
        I:= I+1;
        ];
SetHp(Str+I+1);         \set heap pointer beyond Str (not really needed here)
Text(0, Str);           \show file as a string
]

Output:

include c:\cxpl\codes;  \intrinsic 'code' declarations
string 0;               \use zero-terminated string convention
int  I;
char Str;
[Str:= GetHp;           \starting address of block of local "heap" memory
I:= 0;                  \ [does the exact same thing as Reserve(0)]
loop    [Str(I):= ChIn(1);
        if Str(I) = $1A\EOF\ then [Str(I):= 0;  quit];
        I:= I+1;
        ];
SetHp(Str+I+1);         \set heap pointer beyond Str (not really needed here)
Text(0, Str);           \show file as a string
]

Yorick

This loads foo.txt into lines as an array of strings. Each array element is one line. Each line's trailing newline is removed.

lines = rdfile("foo.txt");

This loads foo.txt into content as a single scalar string, without losing newlines.

f = open("foo.txt", "rb");
raw = array(char, sizeof(f));
_read, f, 0, raw;
close, f;
content = strchar(raw);