//author: Richard Wade Brooks @richard.wade.brooks@gmail.com
//
// This work is dedicated to the public domain under CC0 1.0.
// You may use, modify, and distribute it without restriction.
// Deed - CC0 1.0 Universal - Creative Commons

fn main() {
//if connected to terminal use color in stderr outputs
let mut on_console: bool;
on_console = stderr_is_terminal();
if on_console {
//eprintln!("\x1b[91mcolor in stderr\x1b[0m"); //red
//eprintln!("\x1b[92mcolor in stderr\x1b[0m"); //green
//eprintln!("\x1b[93mcolor in stderr\x1b[0m"); //yellow
//eprintln!("\x1b[94mcolor in stderr\x1b[0m"); //blue
eprintln!("\x1b[95mcolor in stderr\x1b[0m"); //purple
//eprintln!("\x1b[96mcolor in stderr\x1b[0m"); //cyan
//eprintln!("\x1b[97mcolor in stderr\x1b[0m"); //white
} else {
eprintln!("not connected to terminal");
}

println!("\n\n\n");

on_console = stdout_is_terminal();

if on_console {
    println!("stdout is connected to a terminal")
} else {
    println!("stdout is connected to a file or pipe")
}

on_console = stderr_is_terminal();
if on_console {
    println!("stderr is connected to a terminal")
} else {
    println!("stderr is connected to a file or pipe")
}
on_console = stdin_is_terminal();
if on_console {
    println!("stdin is connected to a terminal")
} else {
    println!("stdin is connected to a file or pipe")
}

}

//----------------------------------------------------------

fn stderr_is_terminal() -> bool {
use std::io::{self, IsTerminal};
let on_console = io::stderr().is_terminal();
return on_console;
}

fn stdout_is_terminal() -> bool {
use std::io::{self, IsTerminal};
let on_console = io::stdout().is_terminal();
return on_console;
}

fn stdin_is_terminal() -> bool {
use std::io::{self, IsTerminal};
let on_console = io::stdin().is_terminal();
return on_console;
}

/*
How to test from a bash shell

Save this helper script as test_terminal_modes.sh

#!/usr/bin/env bash

set -u

echo
echo "1) Normal terminal"
echo "Command: ./stream_env"
./stream_env

echo
echo "2) stdin redirected from file"
echo "Command: ./stream_env < test.log"
./stream_env < test.log

echo
echo "3) stdout and stderr redirected to file"
echo "Command: ./stream_env > out.log 2>&1"
./stream_env > out.log 2>&1
echo "Contents of out.log:"
cat out.log

echo
echo "4) stdin piped from another program"
echo "Command: echo hello | ./stream_env"
echo hello | ./stream_env

echo
echo "5) stdout piped to another program"
echo "Command: ./stream_env | cat"
./stream_env | cat

echo
echo "6) stdout and stderr both piped"
echo "Command: ./stream_env 2>&1 | cat"
./stream_env 2>&1 | cat

echo
echo "7) full pipeline"
echo "Command: echo hello | ./stream_env | cat"
echo hello | ./stream_env | cat

Make it executable:
chmod +x test_terminal_modes.sh

Run it:
./test_terminal_modes.sh

Expected results

1. ./stream_env

   stdin is_terminal: true
   stdout is_terminal: true
   stderr is_terminal: true

2. ./stream_env < test.log

   stdin is_terminal: false
   stdout is_terminal: true
   stderr is_terminal: true

3. ./stream_env > out.log 2>&1

   while running:
   stdin is_terminal: true
   stdout is_terminal: false
   stderr is_terminal: false

   those lines go into out.log, not to the screen

4. echo hello | ./stream_env

   stdin is_terminal: false
   stdout is_terminal: true
   stderr is_terminal: true

5. ./stream_env | cat

   stdin is_terminal: true
   stdout is_terminal: false
   stderr is_terminal: true

6. ./stream_env 2>&1 | cat

   stdin is_terminal: true
   stdout is_terminal: false
   stderr is_terminal: false

7. echo hello | ./stream_env | cat

   stdin is_terminal: false
   stdout is_terminal: false
   stderr is_terminal: true

Notes

1. Order matters in shell redirection.

   This:
   ./stream_env > out.log 2>&1

   sends stdout to out.log first, then sends stderr to the same place.

   But this:
   ./stream_env 2>&1 > out.log

   sends stderr to the current stdout first, usually the screen,
   and only then sends stdout to out.log.

2. A bare file name at the end of the command is just an argument.

   This:
   ./stream_env 2>&1 test.log

   does not redirect to test.log.
   It passes "test.log" as an argument to the program.

3. stderr is printed with eprintln!, so when stderr is still attached
   to the terminal, it may appear on screen even if stdout is piped.
   */

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