Read entire file

Task

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, in practice 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.

11l

Translation of: Python

File(filename).read()

8th

The "slurp" word will read the entire contents of the file into memory, as-is, and give a "buffer". The ">s" converts that to a string, again "as-is"

"somefile.txt" f:slurp >s

Action!

proc MAIN()
  char array STRING
  open (1,"D:FILE.TXT",4,0)
  inputsd(1,STRING)
  close(1)
return

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.

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)

Amazing Hopper

Hopper only stores 1 BM of characters for each string variable. If the file to be read "all at once" exceeds that size, the file can be read, and every 1MB saved in a row of a dynamic array of strings, using the PUSH instruction for each portion read. In this way, it is possible to work with portions of a file.

For now, only a simple version is shown.

#include <hopper.h>

main:
   s=""
   load str ("archivo.txt") (s)
   println ( "File loaded:\n",s )
exit(0)

Output:

File loaded:
RX/RY,A,B,C,D,E,F,G,H,I,J
fila 1,1,2,3,4,5,6,7.998,8,9.034,10
fila 2,10,20,30,40,50,60,70,80,90,100
fila 3,100,200,300.5,400,500,600,700,800,900,1000
fila 4,5,10,15,20,25,30,35,40,45,50
fila 5,a,b,c,d,e,f,g,h,i,j
fila 6,1,2,3,4,5,6,7,8,9,10

AppleScript

set pathToTextFile to ((path to desktop folder as string) & "testfile.txt")

-- short way: open, read and close in one step
set fileContent to read file pathToTextFile

-- long way: open a file reference, read content and close access
set fileRef to open for access pathToTextFile
set fileContent to read fileRef
close access fileRef

Arturo

contents: read "input.txt"

ATS

There are various functions in the ATS prelude, including this one that is based on fread(3) and returns Strptr1:

val s = fileref_get_file_string (stdin_ref)

Because Strptr1 is a NUL-terminated string, fileref_get_file_string cannot be used for data that contains bytes equal to zero.

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.

AutoIt

$fileOpen = FileOpen("file.txt")
$fileRead = FileRead($fileOpen)
FileClose($fileOpen)

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; 
}

Works with: gawk

#!/usr/bin/awk -f

@include "readfile"

BEGIN {

  str = readfile("file.txt")
  print str

}

BaCon

For string data:

content$ = LOAD$(filename$)

For memory mapped binary data:

binary = BLOAD("somefile.bin")
PRINT "First two bytes are: ", PEEK(binary), " ", PEEK(binary+1)
FREE binary

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

Applesoft BASIC

 100 D$ =  CHR$ (4)
 110 F$ = "INPUT.TXT"
 120  PRINT D$"VERIFY"F$
 130  PRINT D$"OPEN"F$
 140  PRINT D$"READ"F$
 150  ONERR  GOTO 210
 160  GET C$
 170  POKE 216,0
 180 S$ = S$ + C$
 190  PRINT 
 200  GOTO 140
 210  POKE 216,0
 220 EOF =  PEEK (222) = 5
 230  IF  NOT EOF THEN  RESUME 
 240  PRINT D$"CLOSE"F$

Commodore BASIC

10 rem load the entire contents of some text file as a single string variable.
20 rem should avoid reading an entire file at once if the file is large
30 rem ================================
40 print chr$(14) : rem switch to upper+lowercase character set
50 open 4,8,4,"data.txt,seq,read"
60 n=0
70 for i=0 to 1
80 get#4,x$
90 i=st and 64 : rem check for 'end-of-file'
100 if i=0 then a$=a$+x$ : n=n+1
110 if n=255 then i=1 : rem max string length is 255 only
120 next
130 close 4
140 end

BASIC256

f = freefile
open f, "input.txt"
while not eof(f)
    linea$ = readline(f)
    print linea$
end while
close f

OxygenBasic

Two Formats:

string s

'AS FUNCTION
s=GetFile "t.txt"

'AS PROCEDURE
Getfile "t.txt",s

True BASIC

OPEN #2: NAME "input.txt", ORG TEXT, ACCESS INPUT, CREATE OLD
DO
   LINE INPUT #2: linea$
   PRINT linea$
LOOP UNTIL END #2
CLOSE #2
END

Yabasic

open "input.txt" for reading as #1
while not eof(1)
    line input #1 linea$
    print linea$
wend
close #1

Or also

a = open("input.txt")
while not eof(a)
    line input #a linea$
    print linea$
wend

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%

Blue

Linux/x86-64. Reads the entire file via the mmap system call.

global _start

: syscall ( num:eax -- result:eax ) syscall ;

: exit ( status:edi -- noret ) 60 syscall ;
: bye ( -- noret ) 0 exit ;
: die ( err:eax -- noret ) neg exit ;

: unwrap ( result:eax -- value:eax ) dup 0 cmp ' die xl ;
: ordie ( result -- ) unwrap drop ;

: open ( pathname:edi flags:esi -- fd:eax ) 2 syscall unwrap ;
: close ( fd:edi -- ) 3 syscall ordie ;

48 resb stat_buf
8 resb file-size
88 resb padding

: fstat ( fd:edi buf:esi -- ) 5 syscall ordie ;

1 const prot_read
2 const map_private

: mmap ( fd:r8d len:esi addr:edi off:r9d prot:edx flags:r10d -- buf:eax ) 9 syscall unwrap ;
: munmap ( addr:edi len:esi -- ) 11 syscall ordie ;

1 resd fd
0 const read-only

: open-file ( pathname:edi -- ) read-only open fd ! ;
: read-file-size ( -- ) fd @ stat_buf fstat ;
: map-file ( fd len -- buf ) 0 0 prot_read map_private mmap ;
: map-file ( -- buf ) fd @ file-size @ map-file ;
: unmap-file ( buf -- ) file-size @ munmap ;
: close-file ( -- ) fd @ close ;

: open-this-file ( -- ) s" read_entire_file.blue" drop open-file ;

: _start ( -- noret ) 
	open-this-file
	read-file-size
	map-file
	\ do something ...
	unmap-file
	close-file 
	bye 
;

BQN

File related operations are provided under the system namespace •file. More can be seen under here.

•file.Chars "file"
•file.Bytes "file"

# Shorthands:
•FChars "file"
•FBytes "file"

•file.MapBytes returns an equivalent result to •file.Bytes, using a memory-mapped file to load the contents on demand. It can be sliced with ↑ and ↓ to get part of the file without loading the rest. As BQN arrays are immutable, there's no way to write to the file using this result.

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;
}

Memory map

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;
}

Works with: Windows

Memory map on Windows. See MSDN, starting with File Mapping. In practice, it would be necessary to check for errors, and to take care of large files. Also, this example is using a view on the whole file, but it's possible to create a smaller view.

#include <windows.h>
#include <stdio.h>

int main() {
    HANDLE hFile, hMap;
    DWORD filesize;
    char *p;
    
    hFile = CreateFile("mmap_win.c", GENERIC_READ, 0, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
    filesize = GetFileSize(hFile, NULL);
    hMap = CreateFileMapping(hFile, NULL, PAGE_READONLY, 0, 0, NULL);
    p = MapViewOfFile(hMap, FILE_MAP_READ, 0, 0, 0);

    fwrite(p, filesize, 1, stdout);
    
    CloseHandle(hMap);
    CloseHandle(hFile);
    return 0;
}

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");  
        // Can optionally take a second parameter to specify the encoding, e.g. File.ReadAllText("c:\\autoexec.bat", Encoding.UTF8)
    }
}

C++

#include <iostream>
#include <fstream>
#include <string>
#include <iterator>

int main( ) 
{
    if (std::ifstream infile("sample.txt"))
    {
        // construct string from iterator range
        std::string fileData(std::istreambuf_iterator<char>(infile), std::istreambuf_iterator<char>());

        cout << "File has " << fileData.size() << "chars\n";

        // don't need to manually close the ifstream; it will release the file when it goes out of scope
        return 0;
   }
   else 
   {
      std::cout << "file not found!\n";
      return 1;
   }
}

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

The following will read and store the file as a sequence of bytes.

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

The macro with-open-file could be passed :external-format :utf-8 on some implementations (which it would pass on to open) so that reading would occur by unicode character but (file-length stream) would continue to return the number of bytes, not characters, necessary for storing it.

Crystal

The simplest way to read an entire file to a string is by using File.read:

content = File.read("input.txt")
puts content

Output:

Lorem ipsum dolor sit amet, consectetur adipiscing elit nullam.

The encoding is UTF-8 by default, but it can be explicitly specified:

content = File.read("input.txt", "UTF-16")

or

content = File.read("input.txt", encoding: "UTF-16")

File.open allows for more options and closes the file implicitly. Combine it with File#gets_to_end to read the entire file:

content = File.open("input.txt") do |file|
  file.gets_to_end
end

Or no implicit closing at all with File.new:

file = File.new("input.txt")
content = file.gets_to_end
file.close

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.

Déjà Vu

To get a string from a file, you need to explicitly decode the binary blob that is read. Currently only UTF-8 is supported by vu.

local :filecontents !decode!utf-8 !read "file.txt"

E

<file:foo.txt>.getText()

The file is assumed to be in the default encoding.

Ecstasy

A File object in Ecstasy has a contents property, which yields a Byte[] value:

static Byte[] contentsOf(File file) {
    return file.contents;
}

There are also a few ways to obtain the contents of a file at compile-time as a literal instead of reading it at runtime. These examples show how a byte array literal and a string literal can be obtained from two different files, one using a relative path and one using an absolute path:

Byte[] bytes = #./checkmark.ico;
String html  = $/docs/website/index.htm;

The compiler can even include those files as "file objects"; the files are compiled into the compiled form of the Ecstasy module by the compiler, so their contents reflect the state of those files as they were at compile time:

File iconFile = ./checkmark.ico;
File htmlFile = /docs/website/index.htm;

Byte[] bytes = iconFile.contents;
String html  = htmlFile.contents.unpackUtf8();

Elixir

Two solutions in the FileReader namespace. File returns a tuple: {:ok, file} is successful or {:error, reason} if unsuccessful. Errors can be caught and turned into error strings via Erlang's :file.format_error function.

defmodule FileReader do
  # Read in the file
  def read(path) do
    case File.read(path) do
      {:ok, body} ->
        IO.inspect body
      {:error,reason} ->
        :file.format_error(reason)
      end
    end

  # Open the file path, then read in the file
  def bit_read(path) do
    case File.open(path) do
      {:ok, file} ->
        # :all can be replaced with :line, or with a positive integer to specify the number of characters to read.
	IO.read(file,:all)
	  |> IO.inspect
      {:error,reason} ->
	:file.format_error(reason)
    end
  end
end

Emacs Lisp

insert-file-contents does all Emacs' usual character coding, magic file names, decompression, format decoding, etc. (insert-file-contents-literally can avoid that if unwanted.)

(setq my-variable (with-temp-buffer
                    (insert-file-contents "foo.txt")
                    (buffer-string)))

(If an existing buffer is visiting the file, perhaps yet unsaved, it may be helpful to take its contents instead of re-reading the file. find-buffer-visiting can locate such a buffer.)

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 )

Fortran

Reading the entire source file in memory, then printing it. It relies on the SIZE attribute of the INQUIRE statement returning the size of the file in bytes, whereupon the ALLOCATE statement prepares a variable of the right size to receive the whole content. This SIZE facility was introduced with F2003, and prior to F90 there was no ALLOCATE facility: the size of variables was fixed at compile time.

program read_file
    implicit none
    integer :: n
    character(:), allocatable :: s
    
    open(unit=10, file="read_file.f90", action="read", &
         form="unformatted", access="stream")
    inquire(unit=10, size=n)
    allocate(character(n) :: s)
    read(10) s
    close(10)
    
    print "(A)", s
end program

Intel Fortran on Windows

Here is a solution using the Windows API to create a memory map of a file. It is used to print the source code of the program on the console.

program file_win
    use kernel32
    use iso_c_binding
    implicit none
    
    integer(HANDLE) :: hFile, hMap, hOutput
    integer(DWORD) :: fileSize
    integer(LPVOID) :: ptr
    integer(LPDWORD) :: charsWritten
    integer(BOOL) :: s
    
    hFile = CreateFile("file_win.f90" // c_null_char, GENERIC_READ, &
                       0, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL)
    filesize = GetFileSize(hFile, NULL)
    hMap = CreateFileMapping(hFile, NULL, PAGE_READONLY, 0, 0, NULL)
    ptr = MapViewOfFile(hMap, FILE_MAP_READ, 0, 0, 0)
    
    hOutput = GetStdHandle(STD_OUTPUT_HANDLE)
    s = WriteConsole(hOutput, ptr, fileSize, transfer(c_loc(charsWritten), 0_c_intptr_t), NULL)
    s = CloseHandle(hMap)
    s = CloseHandle(hFile)
end program

FreeBASIC

' FB 1.05.0 Win64

Open "input.txt" For Input Encoding "ascii" As #1
Dim fileLen As LongInt = Lof(1) '' get file length in bytes
Dim buffer As String = Space(fileLen) '' allocate a string of size 'fileLen' bytes
Get #1, 1, buffer '' read all data from start of file into the buffer
Print buffer  '' print to console
buffer = ""  '' release memory used by setting buffer to empty
Close #1
Sleep

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"]

FutureBasic

Note: This code goes beyond simply specifying the file to open. It includes a dialog window (openpanel) that allows the user to select a text file to read. Depending on system memory, as many as 4.2 billion characters can be read. The file contents are placed in a convenient scrolling textview. (Did I mention that FutureBasic -- or FB as developers prefer to call it -- is handy for Macintosh development!) Of course, the programmer is free to code his own window and menu options.

_window = 1
begin enum 1
  _scrollView
  _textView
end enum

void local fn BuildWindow
  CGRect r = {0,0,550,400}
  window _window, @"Read Entire File", r
  scrollview _scrollView, r
  ViewSetAutoresizingMask( _scrollView, NSViewWidthSizable + NSViewHeightSizable )
  textview _textView,, _scrollView
end fn

local fn ReadTextFile
  CFStringRef string
  CFURLRef url = openpanel 1, @"Select text file..."
  if ( url )
    string = fn StringWithContentsOfURL( url, NSUTF8StringEncoding, NULL )
    TextSetString( _textView, string )
  else
    // user cancelled
  end if
end fn

fn BuildWindow
fn ReadTextFile

HandleEvents

Gambas

Public Sub Form_Open()
Dim sFile As String

sFile = File.Load(User.home &/ "file.txt")

End

GAP

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

Genie

[indent=4]
/*
   Read entire file, in Genie

   valac readEntireFile.gs
   ./readEntireFile [filename]
*/

init

    fileName:string
    fileContents:string
    fileName = (args[1] is null) ? "readEntireFile.gs" : args[1]

    try
        FileUtils.get_contents(fileName, out fileContents)
    except exc:Error
        print "Error: %s", exc.message
        return

    stdout.printf("%d bytes read from %s\n", fileContents.length, fileName)

Output:

prompt$ valac readEntireFile.gs
prompt$ ./readEntireFile
443 bytes read from readEntireFile.gs
prompt$ ./readEntireFile nofile
Error: Failed to open file ?nofile?: No such file or directory
prompt$ ./readEntireFile leapYear.gs
291 bytes read from leapYear.gs

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 on OSes with a mmap syscall (e.g. Unix-like). The following prints the contents of "file". (The included "build constraint" prevents this from being compiled on architectures known to lack syscall.Mmap, another source file with the opposite build constraint could use ioutil.ReadFile as above).

// +build !windows,!plan9,!nacl // These lack syscall.Mmap

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

   require 'files'         NB. not needed for J7 & later
   var=: fread '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.

Jakt

fn main() {
    let filename = "Read_entire_file.jakt"
    mut file = File::open_for_reading(filename)
    mut builder = StringBuilder::create()
    for byte in file.read_all() {
        builder.append(byte)
    }
    let contents = builder.to_string()
    println("{}", contents)
}

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);
        in.close();
        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);
	}
}

Works with: Java version 11+

Java 11 added the method readString:

import java.nio.charset.StandardCharsets;
import java.nio.file.Files;

public class ReadAll {
    public static void main(String[] args) {
        System.out.print(Files.readString(Path.of(args[0], StandardCharsets.UTF_8)));
    }
}

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);
}

jq

The . filter will read in a file of raw text, e.g. if the file is named input.txt and we wanted to emit it as a single JSON string:

jq -R -s . input.txt

In practice, this is probably not very useful. It would be more typical to collect the raw lines into an array of JSON strings.

If it is known that the lines are delimited by a single "newline" character, then one could simply pipe from one jq command to another:

jq -R . input.txt | jq -s .

Equivalently:

jq -R -s 'split("\n")' input.txt

Other cases can be similarly handled.

Jsish

var contents = File.read("filename")

From the shell:

Output:

prompt$ jsish
Jsish interactive: see 'help [cmd]'
# var contents = File.read("README")
variable
# contents
"Jsi is a small javascript interpreter for embedded-C development.

Internally Jsi emulates Tcl.  The parser and execution engine originate from quad_wheel,

It is being developed under an MIT license.

"

Julia

The built-in function read, when used with a second argument of String, reads the whole file named by its first argument into a string (assuming UTF8 encoding).

read("/devel/myfile.txt", String) # read file into a string

Alternatively, for files that are too large to read into memory without swapping, there are a variety of ways to memory-map the file, for example as an array of bytes:

A = Mmap.mmap(open("/devel/myfile.txt"), Array{UInt8,1})

K

Works with: ngn/k

`c$1:"example.txt"

The following might be more idiomatic, but returns a list of strings, corresponding to the lines of the file, rather than a single string.

0:"example.txt"

KAP

The built-in function io:readFile will read the entire content of the file as a string:

content ← io:readFile "file.txt"

The function io:read can be used to return all the lines in the file as an array:

content ← io:read "file.txt"

Kotlin

import java.io.File

fun main(args: Array<String>) {
    println(File("unixdict.txt").readText(charset = Charsets.UTF_8))
}

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

Lasso

By default, string objects, which are always Unicode, are created with the assumption that the file contains UTF-8 encoded data. This assumption can be changed by settings the file objects’s character encoding value. When reading the data as a bytes object, the unaltered file data is returned.

local(f) = file('foo.txt')
#f->readString

LFE

(set `#(ok ,data) (file:read_file "myfile.txt"))

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

Lingo

----------------------------------------
-- Reads whole file, returns string
-- @param {string} tFile
-- @return {string|false}
----------------------------------------
on readFile (tFile)
  fp = xtra("fileIO").new()
  fp.openFile(tFile, 1)
  if fp.status() then return false
  res = fp.readFile()
  fp.closeFile()
  return res
end

LiveCode

Livecode offers 2 ways:

Using URL

put URL "file:///usr/share/dict/words" into tVar
put the number of lines of tVar

Using file open + read + close

local tFile,tLinecount
put "/usr/share/dict/words" into tFile
open file tFile for text read
read from file tFile until EOF
put the number of lines of it  -- file contents held in "it" variable
close file tFile

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()

M2000 Interpreter

Module checkit {
      \\ prepare a file
      \\ Save.Doc and Append.Doc  to file, Load.Doc and Merge.Doc from file
      document a$
      a$={First Line
            Second line
            Third Line
            Ελληνικά Greek Letters
            }
      Save.Doc a$, "checkthis.txt", 2  ' 2 for UTF-8
      
      Buffer1=Buffer("checkthis.txt")
      Print Len(Buffer1)=Filelen("checkthis.txt")
      b$=String$(Eval$(Buffer1, 0) as UTF8Dec)
      Report b$
      openfile$=FILE$("text file","txt")
      Merge.doc a$, openfile$
      Edit.Doc a$
}
checkit

M4

An approximation to file reading can be had by include() which reads a file as M4 input. If it's inside a define() then the input is captured as a definition. But this is extremely limited since any macro names, parens, commas, quote characters etc in the file will expand and upset the capture.

define(`foo',include(`file.txt'))
defn(`foo')
defn(`foo')

Make

Works with: GNU make

contents := $(shell cat foo.txt)

This is from the GNU Make manual. As noted there, newlines are converted to spaces in the $(contents) variable. This might be acceptable for files which are a list of words anyway.

Maple

First solution:

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

Second solution:

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

Mathematica/Wolfram Language

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)
   ).

Microsoft Small Basic

  v=File.ReadContents(filename)

Nanoquery

import Nanoquery.IO
contents = new(File, "example.txt").readAll()

Neko

/**
 Read entire file
 Tectonics:
   nekoc read-entire-file.neko
   neko read-entire-file
*/

var file_contents = $loader.loadprim("std@file_contents", 1);

try {
  var entire_file = file_contents("read-entire-file.neko");
  $print("Read: ", $ssize(entire_file), " bytes\n");
} catch e {
  $print("Exception: ", e, "\n");
}

Output:

prompt$ nekoc read-entire-file.neko
prompt$ neko read-entire-file.n
Read: 325 bytes

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")

Nim

To read the content of a file specified by its name:

readFile(filename)

To read the contents of an opened file:

readAll(f)

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 = Bytes.create n in
  really_input ic s 0 n;
  close_in ic;
  (s)

We can replace the last line with the one below if we want to return a type string instead of bytes:

  (Bytes.unsafe_to_string 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

Odin

package main

import "core:os"
import "core:fmt"

main :: proc() {
  data, ok := os.read_entire_file("input.txt")
  assert(ok, "Could not open file")
  defer delete(data)

  fmt.print(string(data))
}

Ol

(file->string "filename")

ooRexx

version 1

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

version 2 EXECIO

One can also use EXECIO as it is known from VM/CMS and MVS/TSO:

address hostemu 'execio * diskr "./st.in" (finis stem in.'
Say in.0 'lines in file st.in'
v=''
Do i=1 To in.0
  Say i '>'in.i'<'
  v=v||in.i
  End
say 'v='v
::requires "hostemu" LIBRARY

Output:

E:\>rexx ref
6 lines in file st.in
1 >address hostemu 'execio * diskr "./st.in" (finis stem in.'<
2 >Say in.0<
3 >Do i=1 To in.0<
4 >  Say i '>'in.i'<'<
5 >  End<
6 >::requires "hostemu" LIBRARY<
v=address hostemu 'execio * diskr "./st.in" (finis stem in.'Say in.0Do i=1 To in
.0  Say i '>'in.i'<'  End::requires "hostemu" LIBRARY

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.

Panda

It returns a unicode string of type 'text'.

file:readme.txt .text

PARI/GP

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

readstr() returns a vector of strings which are the file lines, without newlines. They can be concatenated to make a single string.

str = concat(apply(s->concat(s,"\n"), readstr("file.txt")))

Since readstr() returns strings without newlines there's no way to tell whether the last line had a newline or not. This is fine for its intended use on text files, but not good for reading binary files.

Pascal

See TStrignList example of Delphi

Perl

The modern recommended way, is using one of these CPAN modules:

use File::Slurper 'read_text';
my $text = read_text($filename, $data);

use Path::Tiny;
my $text = path($filename)->slurp_utf8;

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

Traditional ways, without CPAN modules:

open my $fh, '<:encoding(UTF-8)', $filename or die "Could not open '$filename':  $!";
my $text;
read $fh, $text, -s $filename;
close $fh;

my $text;
{
  local $/ = undef;
  open my $fh, '<:encoding(UTF-8)', $filename or die "Could not open '$filename':  $!";
  $text = <$fh>;
  close $fh;
}

my $text = do { local( @ARGV, $/ ) = ( $filename ); <> };

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

Memory-mapping

use File::Map 'map_file';
map_file(my $str, "foo.txt");
print $str;

use Sys::Mmap;
Sys::Mmap->new(my $str, 0, 'foo.txt')
  or die "Cannot Sys::Mmap->new: $!";
print $str;

File::Map has the advantage of not requiring an explicit munmap(). Its tie is faster than the tie form of Sys::Mmap too.

Phix

Library: Phix/basics

?get_text(command_line()[2])

Output:

"?get_text(command_line()[2])\r\n"

The value returned by get_text is actually a string containing raw binary data (no \r\n -> \n substitution, even when the file is opened in text mode) and is not limited to text files.
There is no builtin method for handling different encodings, but demo\edita handles all such files with ease, including the nifty little encoding drop-down on the open/close dialog.

PHP

Read as string

file_get_contents($filename)

Read as array, one element per line

file($filename)

Picat

The encoding is always UTF-8. Anything more than a small file will cause a buffer overflow.

Works with: Picat

main(Args) =>
    File = Args[1],
    String = read_file_chars(File).

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();

would be the generic way of reading an entire file, but there is also a special function for it:

string content=Stdio.read_file("foo.txt");

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"

Prolog

Read a text file. The third argument of read_file_to_string could be options.

Works with: SWI Prolog

:- initialization(main).

main :-
    current_prolog_flag(argv, [File|_]),
    read_file_to_string(File, String, []).

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()

Python docs recommend dealing with files using the with statement:

with open(filename) as f:
    data = f.read()

Starting in Python 3.4, we can use pathlib to reduce boilerplate:

from pathlib import Path

any_string = Path(filename).read_text(encoding='utf-8')
any_binary_data = Path(filename).read_bytes()

Quackery

sharefile takes a file name in a string as an argument, appends a file path if there is one on the ancillary stack filepath, and returns the contents of the file as a string, and 1 (i.e. true) if the file exists. If the file does not exist it returns the name of the file and 0 (i.e. false).

$ "myfile.txt" sharefile

Q

q)file:read0`:file.txt
"First line of file"
"Second line of file"
""

R

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

Racket

(file->string "foo.txt")

Raku

(formerly Perl 6)

Works with: Rakudo version 2010.07

my $string = slurp 'sample.txt';

The default encoding is UTF-8. The :enc adverb can be used to specify a different one:

my $string = slurp 'sample.txt', :enc<UTF-16>;

IO::Path objects also provide slurp as a method:

my $string = 'sample.txt'.IO.slurp;

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

here 'input.txt file:slurp

REXX

using LINEIN

/*REXX program reads an entire file line-by-line  and  stores it as a continuous string.*/
parse arg iFID .                                 /*obtain optional argument from the CL.*/
if iFID==''  then iFID= 'a_file'                 /*Not specified?  Then use the default.*/
$=                                               /*a string of file's contents (so far).*/
             do  while lines(iFID)\==0           /*read the file's lines until finished.*/
             $=$ || linein(iFID)                 /*append a (file's) line to the string,*/
             end   /*while*/                     /*stick a fork in it,  we're all done. */

using CHARIN

Note that CRLF are in the resulting string.

/*REXX program reads a file and stores it as a continuous character str.*/
Parse Version v
iFID = 'st.in'                         /*name of the input file.        */
If left(v,11)='REXX-Regina' |,
   left(v,11)='REXX-ooRexx' Then Do
  len=chars(iFid)                      /*size of the file               */
  v = charin(iFid,,len)                /*read entire file               */
  End
Else Do                                /* for other Rexx Interpreters   */
  v=''
  Do while chars(iFid)>0               /* read the file chunk by chunk  */
    v=v||charin(iFid,,500)
    End
  End
say 'v='v
say 'length(v)='length(v)

Output:

E:\>rexx refc
v=line 1 of 3
line 2 of 3
line 3 of 3

length(v)=39

Ring

# Read the file
cStr = read("myfile.txt")
# print the file content
See cStr

Also in one line we can read and print the file content.

cStr = read("myfile.txt")   See cStr

We can avoid the string, but it's required in the task.

See read("myfile.txt")

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}

Run BASIC

open DefaultDir$ + "/public/test.txt" for binary as #f
fileLen = LOF(#f)
a$ = input$(#f, fileLen)
print a$
close #f

Rust

use std::fs::File;
use std::io::Read;

fn main() {
    let mut file = File::open("somefile.txt").unwrap();

    let mut contents: Vec<u8> = Vec::new();
    // Returns amount of bytes read and append the result to the buffer
    let result = file.read_to_end(&mut contents).unwrap();
    println!("Read {} bytes", result);

    // To print the contents of the file
    let filestr = String::from_utf8(contents).unwrap();
    println!("{}", filestr);
}

Scala

Library: Scala

object TextFileSlurper extends App {
  val fileLines =
    try scala.io.Source.fromFile("my_file.txt", "UTF-8").mkString catch {
      case e: java.io.FileNotFoundException => e.getLocalizedMessage()
    }
}

Scheme

Uses SRFI-13:

(with-input-from-file "foo.txt"
  (lambda ()
    (reverse-list->string
     (let loop ((char (read-char))
                (result '()))
       (if (eof-object? char)
           result
           (loop (read-char) (cons char result)))))))

Works with Chicken Scheme:

(with-input-from-file "foo.txt" read-string)

In GNU Guile, with decoding into Unicode code points:

(use-modules (ice-9 textual-ports))
(call-with-input-file "foo.txt" get-string-all)

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;

SenseTalk

Put file "~/Documents/myFile.txt" into  TestFile
put testFile

Sidef

Reading an entire file as a string, can be achieved with the FileHandle.slurp() method, as illustrated bellow:

var file = File.new(__FILE__);
var content = file.open_r.slurp;
print content;

Starting with version 2.30, File.read() can do the same:

var file = File(__FILE__)
var content = file.read(:utf8)
print content

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

Sparkling

let contents = readfile("foo.txt");

SPL

text = #.readtext("filename.txt")

Standard ML

(* string -> string *)
fun readFile path =
  (fn strm =>
    TextIO.inputAll strm before TextIO.closeIn strm) (TextIO.openIn path)

</syntaxhighlight>

Stata

It's possible to get the entire content as an array of lines with cat. However, here we want a single string. See fopen and related functions.

mata
f = fopen("somedata.txt", "r")
fseek(f, 0, 1)
n = ftell(f)
fseek(f, 0, -1)
s = fread(f, n)
fclose(f)
end

Swift

Works with: Swift version 1

import Foundation

let path = "~/input.txt".stringByExpandingTildeInPath
if let string = String(contentsOfFile: path, encoding: NSUTF8StringEncoding) {
  println(string) // print contents of file
}

Works with: Swift version 5

import Foundation

let path = "input.txt"
do
{
	let string = try String(contentsOfFile: path, encoding: String.Encoding.utf8)
	print(string) // print contents of file
}
catch
{
	print("error occured: \(error)")
}

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]

Ursa

decl string contents
decl file f
f.open "filename.txt"
set contents (f.readall)

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

Works with: Visual Basic version 5

Works with: Visual Basic version 6

Declare Function MultiByteToWideChar Lib "kernel32.dll" ( _
     ByVal CodePage As Long, _
     ByVal dwFlags As Long, _
     ByVal lpMultiByteStr As Long, _
     ByVal cchMultiByte As Long, _
     ByVal lpWideCharStr As Long, _
     ByVal cchWideChar As Long) As Long
Const CP_UTF8 As Long = 65001

Sub Main()
Dim fn As Integer
Dim i As Long
Dim b() As Byte
Dim s As String

  fn = FreeFile()
  Open "c:\test.txt" For Binary Access Read As #fn
  ReDim b(0 To (LOF(fn) - 1))
  Get #fn, 1, b()
  
  If b(0) = &HFF And b(1) = &HFE Then
  'UTF-16, little-endian
    ReDim b(0 To (LOF(fn) - 3))
    Get #fn, 3, b()
    s = b()
  ElseIf b(0) = &HEF And b(1) = &HBB And b(2) = &HBF Then
  'UTF-8
    i = MultiByteToWideChar(CP_UTF8, 0&, VarPtr(b(3)), LOF(fn) - 3, StrPtr(s), 0)
    s = Space$(i)
    i = MultiByteToWideChar(CP_UTF8, 0&, VarPtr(b(3)), LOF(fn) - 3, StrPtr(s), Len(s))
  Else
  'assume ANSI
    s = StrConv(b(), vbUnicode)
  End If
  Close #fn
  Debug.Print s
End Sub

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

Wart

with infile "x"
  with outstring
    whilet line (read_line)
      prn line

Wren

Wren's File.Read(path) static method reads the entire contents of the file at path and returns it as a string.

As per the documentation: "No encoding or decoding is done. If the file is UTF-8, then the resulting string will be a UTF-8 string. Otherwise, it will be a string of bytes in whatever encoding the file uses."

For the following script, a file called "input.txt" has been created which contains the string "abcdefghijklmnopqrstuvwxyz".

import "io" for File

System.print(File.read("input.txt"))

Output:

abcdefghijklmnopqrstuvwxyz

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
]

Xtend

package com.rosetta.example

import java.io.File
import java.io.PrintStream

class ReadFile {
    def static main( String ... args ) {
        val content = new String(Files.readAllBytes(Paths.get("file.txt")))
    }
}

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);

Zig

Works with: Zig version 0.10.x

Works with: Zig version 0.11.x

Works with: Zig version 0.12.0-dev.1604+caae40c21

const std = @import("std");

const File = std.fs.File;

pub fn main() (error{OutOfMemory} || File.OpenError || File.ReadError)!void {
    var gpa: std.heap.GeneralPurposeAllocator(.{}) = .{};
    defer _ = gpa.deinit();
    const allocator = gpa.allocator();

    const cwd = std.fs.cwd();

    var file = try cwd.openFile("input_file.txt", .{ .mode = .read_only });
    defer file.close();

    const file_content = try file.readToEndAlloc(allocator, comptime std.math.maxInt(usize));
    defer allocator.free(file_content);

    std.debug.print("Read {d} octets. File content:\n", .{file_content.len});
    std.debug.print("{s}", .{file_content});
}

Using mmap

When linking libc, will use libc mmap (or mmap64) call. Otherwise uses namespace supplied by user or std (includes support for Windows, among other things, so no need to write two separate versions like in C).

const std = @import("std");

const File = std.fs.File;

pub fn main() (File.OpenError || File.SeekError || std.os.MMapError)!void {
    const cwd = std.fs.cwd();

    var file = try cwd.openFile("input_file.txt", .{ .mode = .read_only });
    defer file.close();

    const file_size = (try file.stat()).size;

    const file_content = try std.os.mmap(null, file_size, std.os.PROT.READ, std.os.MAP.PRIVATE, file.handle, 0);
    defer std.os.munmap(file_content);

    std.debug.print("Read {d} octets. File content:\n", .{file_content.len});
    std.debug.print("{s}", .{file_content});
}

zkl

data := File("foo.txt","r").read()

The file parameters are the same as C's