Check input device is a terminal

Check input device is a terminal 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.

The task is to demonstrate how to check whether the input device is a terminal or not.

See also: Check output device is a terminal

C

Use isatty() on file descriptor to determine if it's a TTY. To get the file descriptor from a FILE* pointer, use fileno: <lang c>#include <unistd.h> //for isatty()

1. include <stdio.h> //for fileno()

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

Output:

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

D

<lang 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.");

}</lang>

Output:

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

OCaml

<lang ocaml>let () =

 print_endline (
   if Unix.isatty Unix.stdin
   then "Input comes from tty."
   else "Input doesn't come from tty."
 )</lang>

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.

Perl

<lang perl>use strict; use warnings; use 5.010; if (-t) {

   say "Input comes from tty.";

} else {

   say "Input doesn't come from tty.";

}</lang>

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

Perl 6

<lang perl6>say $*IN.t ?? "Input comes from tty." !! "Input doesn't come from tty.";</lang>

$ perl6 istty.p6
Input comes from tty.
$ true | perl6 istty.p6
Input doesn't come from tty.

Python

<lang python>from sys import stdin if stdin.isatty():

   print("Input comes from tty.")

else:

   print("Input doesn't come from tty.")</lang>

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

Racket

<lang racket> (terminal-port? (current-input-port)) </lang>

REXX

<lang 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.*/

</lang>

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. <lang tcl>if {[catch {fconfigure stdin -mode}]} {

   puts "Input doesn't come from tty."

} else {

   puts "Input comes from tty."

}</lang> Demonstrating:

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