Copy stdin to stdout

Copy stdin to stdout is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

Create an executable file that copies stdin to stdout, or else a script that does so through the invocation of an interpreter at the command line.

Ada

<lang Ada>with Ada.Text_IO;

procedure Copy_Stdin_To_Stdout is

  use Ada.Text_IO;
  C : Character;

begin

  while not End_Of_File loop
     Get_Immediate (C);
     Put (C);
  end loop;

end Copy_Stdin_To_Stdout;</lang>

Aime

<lang aime>file f; data b; f.stdin; while (f.b_line(b) ^ -1) {

   o_(b, "\n");

}</lang>

ALGOL 68

Works with: ALGOL 68G version Any - tested with release 2.8.3.win32

<lang algol68>BEGIN

   BOOL at eof := FALSE;
   # set the EOF handler for stand in to a procedure that sets "at eof" to true #
   # and returns true so processing can continue                                #                               
   on logical file end( stand in, ( REF FILE f )BOOL: at eof := TRUE );
   # copy stand in to stand out                                                 #
   WHILE STRING line; read( ( line, newline ) ); NOT at eof DO write( ( line, newline ) ) OD

END</lang>

AWK

Using the awk interpreter, the following command uses the pattern // (which matches anything) with the default action (which is to print the current line) and so copy lines from stdin to stdut. <lang AWK>awk "//"</lang>

C

<lang C>

1. include <stdio.h>

int main(){

 char c;
 while ( (c=getchar()) != EOF ){
   putchar(c);
 }
 return 0;

} </lang>

C++

<lang cpp>#include <iostream>

1. include <iterator>

int main() {

   using namespace std;
   noskipws(cin);
   copy(
       istream_iterator<char>(cin),
       istream_iterator<char>(),
       ostream_iterator<char>(cout)
   );
   return 0;

}</lang>

D

<lang d>import std.stdio;

void main() {

   foreach (line; stdin.byLine) {
       writeln(line);
   }

}</lang>

Go

<lang go>package main

import (

   "bufio"
   "io"
   "os"

)

func main() {

   r := bufio.NewReader(os.Stdin)
   w := bufio.NewWriter(os.Stdout)
   for {
       b, err := r.ReadByte()       
       if err == io.EOF {
           return
       }
       w.WriteByte(b)
       w.Flush()
   }   

}</lang>

Haskell

<lang Haskell>main = interact id </lang>

Java

Copies until no more input. <lang java> import java.util.Scanner;

public class CopyStdinToStdout {

   public static void main(String[] args) {
       try (Scanner scanner = new Scanner(System.in);) {
           String s;
           while ( (s = scanner.nextLine()).compareTo("") != 0 ) {
               System.out.println(s);
           }
       }
   }

} </lang>

Output:

Output interleaved. Stdin and Stdout are same window.

Line 1.
Line 1.
Line 2.
Line 2.

Julia

<lang Julia>while !eof(stdin)

   write(stdout, read(stdin, UInt8))

end</lang>

Kotlin

<lang scala>fun main() {

   var c: Int
   do {
       c = System.`in`.read()
       System.out.write(c)
   } while (c >= 0)

}</lang>

Lua

lua -e 'for x in io.lines() do print(x) end'

Mercury

<lang Mercury>

- module stdin_to_stdout.

- interface.

- import_module io.

- pred main(io::di, io::uo) is det.

%-----------------------------------------------------------------------------% %-----------------------------------------------------------------------------%

- implementation.

- import_module char.

- import_module list.

- import_module string.

%-----------------------------------------------------------------------------%

main(!IO) :-

   io.read_line_as_string(Result, !IO),
   (
       Result = ok(Line),
       io.write_string(Line, !IO),
       main(!IO)
   ;
       Result = eof
   ;
       Result = error(Error),
       io.error_message(Error, Message),
       io.input_stream_name(StreamName, !IO),
       io.progname("stdin_to_stdout", ProgName, !IO),
       io.write_strings([
           ProgName, ": ",
           "error reading from `", StreamName, "': \n\t",
           Message, "\n"
       ], !IO)
   ).

%-----------------------------------------------------------------------------% </lang>

Nim

<lang nim>stdout.write readAll(stdin)</lang>

OCaml

<lang ocaml>try

 while true do
   output_char stdout (input_char stdin)
 done

with End_of_file -> ()</lang>

Perl

<lang perl> perl -pe </lang>

Phix

<lang Phix>while true do

   integer ch = wait_key()
   if ch=#1B then exit end if
   puts(1,ch)

end while</lang>

PicoLisp

<lang PicoLisp>(in NIL (echo))</lang>

Prolog

<lang Prolog> %File: stdin_to_stdout.pl

- initialization(main).

main :- repeat, get_char(X), put_char(X), X == end_of_file, fail. </lang>

Invocation at the command line (with Swi-prolog): <lang sh> swipl stdin_to_stdout.pl </lang>

Python

python -c 'import sys; sys.stdout.write(sys.stdin.read())'

R

Rscript -e 'cat(readLines(file("stdin")))'

Racket

<lang racket>#lang racket

(let loop ()

 (match (read-char)
   [(? eof-object?) (void)]
   [c (display c)
      (loop)]))</lang>

Raku

(formerly Perl 6) When invoked at a command line: Slightly less magical than Perl / sed. The p flag means automatically print each line of output to STDOUT. The e flag means execute what follows inside quotes. ".lines" reads lines from the assigned pipe (file handle), STDIN by default.

<lang perl6>perl6 -pe'.lines'</lang>

When invoked from a file: Lines are auto-chomped, so need to re-add newlines (hence .say rather than .print) <lang perl6>.say for lines</lang>

REXX

In the REXX language,   the   STDIN   (default input stream)   is normally the console,   and the   STDOUT   (default output stream)   is normally the console.   So for REXX, this task equates to copying data from the console to itself. <lang rexx>/*REXX pgm copies data from STDIN──►STDOUT (default input stream──►default output stream*/

 do while chars()\==0                           /*repeat loop until no more characters.*/
 call charin  , x                               /*read  a char from the  input stream. */
 call charout , x                               /*write "   "    "   "   output   "    */
 end   /*while*/                                /*stick a fork in it,  we're all done. */</lang>

Rust

<lang Rust>use std::io;

fn main() {

   io::copy(&mut io::stdin().lock(), &mut io::stdout().lock());

}</lang>

Scheme

<lang scheme> (do ((c (read-char) (read-char)))

   ((eof-object? c) 'done)
 (display c))

</lang>

sed

<lang sh> sed -e </lang>

zkl

<lang zkl>zkl --eval "File.stdout.write(File.stdin.read())"</lang>