Read entire file

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Task
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.

Contents

[edit] Ada

[edit] 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.

[edit] 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.

[edit] 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.

[edit] 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)

[edit] 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;
}

[edit] 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

[edit] 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:

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

[edit] Bracmat

get'(filename,STR):?myString

[edit] 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]

[edit] Brat

include :file
 
file.read file_name

[edit] 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;
}

[edit] 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 ;
}
}
 

[edit] 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");
}
}
 

[edit] 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")

[edit] 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)

[edit] Common Lisp

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

[edit] 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");
}

[edit] 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.

[edit] 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"

[edit] E

<file:foo.txt>.getText()

The file is assumed to be in the default encoding.

[edit] Erlang

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

This reads the entire file into a binary object.

[edit] 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
 

[edit] 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)

[edit] 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

[edit] 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")
}
}
 

[edit] Forth

Works with: GNU Forth
s" foo.txt" slurp-file   ( str len )

[edit] 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"]
 

[edit] GAP

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

[edit] 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))
}

[edit] Groovy

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

[edit] GUISS

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

[edit] 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

[edit] 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

[edit] 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.

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

[edit] 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.

[edit] 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);
}
}

[edit] 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);
}
 

[edit] Julia

The built-in function readall reads into a string (assuming UTF8 encoding), or you can also read into an array of bytes:

readall("/devel/myfile.txt") # read file into a string
open(readbytes, "/devel/myfile.txt") # read file into an array of bytes

Alternatively, there are a variety of ways to memory-map the file, here as an array of bytes:

f = open("/devel/myfile.txt", "r")
A = mmap_array(Uint8, (filesize("/devel/myfile.txt"),), f)

[edit] 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.
LabVIEW Read entire file.png

[edit] Lang5

'foo.txt slurp

[edit] 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

[edit] 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

[edit] 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()
 

[edit] Maple

First solution:

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

Second solution:

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

[edit] Mathematica

Import["filename","String"]

[edit] 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);

[edit] 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)
).

[edit] 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
 

[edit] NewLISP

(read-file "filename")

[edit] Nimrod

readFile(filename)

[edit] Objeck

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

[edit] 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);
}
 

[edit] 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

[edit] 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
 

[edit] OxygenBasic

Two Formats:


string s

'AS FUNCTION

s=GetFile "t.txt"

'AS PROCEDURE

Getfile "t.txt",s

[edit] 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.

[edit] 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");

[edit] Pascal

See TStrignList example of Delphi

[edit] 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

[edit] Perl 6

Works with: Rakudo version 2010.07
my $string = slurp 'sample.txt';

[edit] PHP

file_get_contents($filename)

[edit] 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.

[edit] Pike

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

[edit] PL/I

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

[edit] 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"

[edit] 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

[edit] 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()

[edit] R

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

[edit] Racket

(file->string "foo.txt")

[edit] 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

[edit] 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
 

[edit] REBOL

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

[edit] Retro

with files'
here "input.txt" slurp

[edit] 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.*/

[edit] 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}

[edit] Run BASIC

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

[edit] Rust

// -*- rust v0.9 -*-
use std::str;
use std::io::File;
 
fn main() {
let path = Path::new("hello.txt");
let mut file = File::open(&path);
 
let contents = str::from_utf8_owned(file.read_to_end());
println(contents);
}
 
 

[edit] Scala

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

[edit] 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)

[edit] 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;

[edit] Smalltalk

Works with: Pharo
(StandardFileStream oldFileNamed: 'foo.txt') contents
Works with: Smalltalk/X
'foo.txt' asFilename contentsAsString

[edit] 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

[edit] 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

[edit] TUSCRIPT

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

[edit] 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.

[edit] 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]

[edit] Vala

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

[edit] 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

[edit] 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")

[edit] 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

[edit] Wart

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

[edit] 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
]

[edit] 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);

[edit] zkl

data := File("foo.txt","r").read()

The file parameters are the same as C's

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