Check input device is a terminal

Demonstrate how to check whether the input device is a terminal or not.

Check input device is a terminal
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Task

Related task

•   Check output device is a terminal

Ada

Works with: GNAT

We use the interface to C library functions isatty() and fileno().

with Ada.Text_IO;          use Ada.Text_IO;
with Interfaces.C_Streams; use Interfaces.C_Streams;

procedure Test_tty is
begin
   if Isatty(Fileno(Stdin)) = 0 then
      Put_Line(Standard_Error, "stdin is not a tty.");
   else
      Put_Line(Standard_Error, "stdin is a tty.");
   end if;
end Test_tty;

Output:

$ ./test_tty 
stdin is a tty.
$ ./test_tty < /dev/null
stdin is not a tty.

BaCon

terminal = isatty(0)
PRINT terminal

Output:

prompt$ bacon -q istty.bac
Converting 'istty.bac'... done, 4 lines were processed in 0.002 seconds.
Compiling 'istty.bac'... cc  -c istty.bac.c
cc -o istty istty.bac.o    -lm
Done, program 'istty' ready.
prompt$ ./istty
1
prompt$ ./istty <<<"testing"
0

C

Use isatty() on file descriptor to determine if it's a TTY. To get the file descriptor from a FILE* pointer, use fileno:

#include <unistd.h>	//for isatty()
#include <stdio.h>	//for fileno()

int main(void)
{
	puts(isatty(fileno(stdin))
		? "stdin is tty"
		: "stdin is not tty");
	return 0;
}

Output:

$ ./a.out
stdin is tty
$ ./a.out < /dev/zero
stdin is not tty
$ echo "" | ./a.out
stdin is not tty

COBOL

Works with GnuCOBOL.

      *>
      *> istty, check id fd 0 is a tty
      *> Tectonics: cobc -xj istty.cob
      *>            echo "test" | ./istty
      *>
       identification division.
       program-id. istty.

       data division.
       working-storage section.
       01 rc usage binary-long.

       procedure division.
       sample-main.

       call "isatty" using by value 0 returning rc
       display "fd 0 tty: " rc

       call "isatty" using by value 1 returning rc
       display "fd 1 tty: " rc upon syserr

       call "isatty" using by value 2 returning rc
       display "fd 2 tty: " rc

       goback.
       end program istty.

DISPLAY for fd 1 is directed to SYSERR to get some output during the various trials.

Output:

prompt$ cobc -xj istty.cob
fd 0 tty: +0000000001
fd 1 tty: +0000000001
fd 2 tty: +0000000001
prompt$ echo "test" | ./istty
fd 0 tty: +0000000000
fd 1 tty: +0000000001
fd 2 tty: +0000000001
prompt$ echo "test" | ./istty >/dev/null
fd 1 tty: +0000000000
prompt$ echo "test" | ./istty 2>/dev/tty
fd 0 tty: +0000000000
fd 1 tty: +0000000001
fd 2 tty: +0000000001
prompt$ echo "test" | ./istty 2>/dev/null
fd 0 tty: +0000000000
fd 2 tty: +0000000000

Common Lisp

Works with: SBCL

(with-open-stream (s *standard-input*)
  (format T "stdin is~:[ not~;~] a terminal~%" 
          (interactive-stream-p s)))

Output:

$ sbcl --script rc.lisp
stdin is a terminal
$ sbcl --script rc.lisp < /dev/zero
stdin is not a terminal
$ echo "" | sbcl --script rc.lisp
stdin is not a terminal

Crystal

File.new("testfile").tty?   #=> false
File.new("/dev/tty").tty?   #=> true
STDIN.tty?  #=> true

D

import std.stdio;

extern(C) int isatty(int);

void main() {
    if (isatty(0))
        writeln("Input comes from tty.");
    else
        writeln("Input doesn't come from tty.");
}

Output:

C:\test
Input comes from tty.
C:\test < in.txt
Input doesn't come from tty.

FreeBASIC

Open Cons For Input As #1
' Open Cons abre los flujos de entrada (stdin) o salida (stdout) estándar 
' de la consola para leer o escribir. 

If Err Then
    Print "Input doesn't come from tt."
Else
    Print "Input comes from tty."
End If  
Close #1
Sleep

FutureBasic

include "NSLog.incl"

BeginCCode
  if (isatty(fileno(stdin)))
  NSLog( @"stdin is connected to a terminal" );
  else
  NSLog( @"stdin is NOT connected to a terminal" );
EndC

HandleEvents

Output:

stdin is NOT connected to a terminal

Go

Library: Go sub-repositories

package main

import (
    "golang.org/x/crypto/ssh/terminal"
    "fmt"
    "os"
)

func main() {
    if terminal.IsTerminal(int(os.Stdin.Fd())) {
        fmt.Println("Hello terminal")
    } else {
        fmt.Println("Who are you?  You're not a terminal.")
    }
}

Output:

> hello
Hello terminal
> hello </dev/null
Who are you?  You're not a terminal.

Haskell

Example uses unix package:

module Main (main) where
 
import           System.Posix.IO (stdInput)
import           System.Posix.Terminal (queryTerminal)
 
main :: IO ()
main = do
    isTTY <- queryTerminal stdInput
    putStrLn $ if isTTY
                then "stdin is TTY"
                else "stdin is not TTY"

Jsish

/* Check input device is a terminal, in Jsish */
;Interp.conf().subOpts.istty;

/*
=!EXPECTSTART!=
Interp.conf().subOpts.istty ==> false
=!EXPECTEND!=
*/

Output:

prompt$ jsish
Jsish interactive: see 'help [cmd]' or 'history'.  \ cancels > input.  ctrl-c aborts running script.
jsi> Interp.conf().subOpts.istty;
true
jsi>
prompt$ jsish --U checkInputDevice.jsi
Interp.conf().subOpts.istty ==> false

Julia

if isa(STDIN, Base.TTY)
    println("This program sees STDIN as a TTY.")
else
    println("This program does not see STDIN as a TTY.")
end

Output:

This program sees STDIN as a TTY.

Kotlin

Works with: Ubuntu version 14.04

// Kotlin Native version 0.5

import platform.posix.*

fun main(args: Array<String>) {
    if (isatty(STDIN_FILENO) != 0)
        println("stdin is a terminal")
    else
        println("stdin is not a terminal") 
}

Output:

stdin is a terminal

Nemerle

There is no explicit way (ie isatty())to do this; however, if we assume that standard input is a terminal, we can check if the input stream has been redirected (presumably to something other than a terminal).

def isTerm = System.Console.IsInputRedirected;

Nim

Using function "isatty" of standard module "terminal" which accepts a File as argument.

import terminal

echo if stdin.isatty: "stdin is a terminal" else: "stdin is not a terminal"

Output:

Command: ./check_input_dev
Result: stdin is a terminal

Command: ./check_input_dev <somefile
Result: stdin is not a terminal

OCaml

let () =
  print_endline (
    if Unix.isatty Unix.stdin
    then "Input comes from tty."
    else "Input doesn't come from tty."
  )

Testing in interpreted mode:

$ ocaml unix.cma istty.ml
Input comes from tty.
$ echo "foo" | ocaml unix.cma istty.ml
Input doesn't come from tty.

Ol

(define (isatty? fd) (syscall 16 fd 19))
(print (if (isatty? stdin)
   "Input comes from tty."
   "Input doesn't come from tty."))

Perl

use strict;
use warnings;
use 5.010;
if (-t) {
    say "Input comes from tty.";
}
else {
    say "Input doesn't come from tty.";
}

$ perl istty.pl
Input comes from tty.
$ true | perl istty.pl
Input doesn't come from tty.

Phix

without js -- (no input redirection in a browser!)
printf(1,"stdin:%t, stdout:%t, stderr:%t\n",{isatty(0),isatty(1),isatty(2)})

Output:

C:\Program Files (x86)\Phix>p test
stdin:true, stdout:true, stderr:true
C:\Program Files (x86)\Phix>echo hello | p test
stdin:false, stdout:true, stderr:true

Pike

void main()
{
    if(Stdio.Terminfo.is_tty())
	write("Input comes from tty.\n");
    else
        write("Input doesn't come from tty.\n");
}

Output:

$ ./istty.pike
Input comes from tty.
$ echo | ./istty.pike
Input doesn't come from tty.

Python

from sys import stdin
if stdin.isatty():
    print("Input comes from tty.")
else:
    print("Input doesn't come from tty.")

$ python istty.py
Input comes from tty.
$ true | python istty.py
Input doesn't come from tty.

Quackery

Translation of: Python

  [ $ |from sys import stdin
to_stack( 1 if stdin.isatty() else 0)|
    python ]                            is ttyin ( --> b )     

  ttyin if 
    [ say "Looks like a teletype." ] 
  else 
    [ say "Not a teletype." ]

Output:

Looks like a teletype.

Racket

(terminal-port? (current-input-port))

Raku

(formerly Perl 6)

Works with: Rakudo version 2015.12

say $*IN.t ?? "Input comes from tty." !! "Input doesn't come from tty.";

$ raku istty.raku
Input comes from tty.
$ true | raku istty.raku
Input doesn't come from tty.

REXX

/*REXX program determines if input comes from terminal or standard input*/

if queued()  then say 'input comes from the terminal.'
             else say 'input comes from the (stacked) terminal queue.'

                                       /*stick a fork in it, we're done.*/

Ring

# Project  : Check input device is a terminal
 
load "stdlib.ring"

if isWindows()
   write("mycmd.bat","
   @echo off
    timeout 1 2>nul >nul
    if errorlevel 1 (
       echo input redirected
        ) else (
       echo input is console
       )
       ")
    see SystemCmd("mycmd.bat")
ok

Output:

input redirected

Ruby

Example from the docs.

File.new("testfile").isatty   #=> false
File.new("/dev/tty").isatty   #=> true

Rust

/* Uses C library interface */

extern crate libc;

fn main() {
    let istty = unsafe { libc::isatty(libc::STDIN_FILENO as i32) } != 0;
    if istty {
        println!("stdout is tty");
    } else {
        println!("stdout is not tty");
    }
}

Scala

Works with: Ubuntu version 14.04

import org.fusesource.jansi.internal.CLibrary._

object IsATty  extends App {

  var enabled = true

  def apply(enabled: Boolean): Boolean = {
    // We must be on some unix variant..
    try {
      enabled && isatty(STDIN_FILENO) == 1
    }
    catch {
      case ignore: Throwable =>
        ignore.printStackTrace()
        false

    }
  }

    println("tty " + apply(true))
}

Standard ML

val stdinRefersToTerminal : bool = Posix.ProcEnv.isatty Posix.FileSys.stdin

Tcl

Tcl automatically detects whether stdin is coming from a terminal (or a socket) and sets up the channel to have the correct type. One of the configuration options of a terminal channel is -mode (used to configure baud rates on a real serial terminal) so we simply detect whether the option is present.

if {[catch {fconfigure stdin -mode}]} {
    puts "Input doesn't come from tty."
} else {
    puts "Input comes from tty."
}

Demonstrating:

$ tclsh8.5 istty.tcl 
Input comes from tty.
$ tclsh8.5 istty.tcl </dev/null
Input doesn't come from tty.

UNIX Shell

#!/bin/sh

if [ -t 0 ]
then
   echo "Input is a terminal"
else
   echo "Input is NOT a terminal"
fi

Wren

import "io" for Stdin

System.print("Input device is a terminal? %(Stdin.isTerminal ? "Yes" : "No")")

Output:

Input device is a terminal? Yes

zkl

On Unix, check to see if stdin's st_mode is a character device.

const S_IFCHR=0x2000;
fcn S_ISCHR(f){ f.info()[4].bitAnd(S_IFCHR).toBool() }
S_ISCHR(File.stdin).println();

Output:

$ zkl bbb  # from the command line
True
$ zkl bbb < bbb.zkl
False
$ cat bbb.zkl | zkl bbb
False