File descriptors - stdin and stdout - isTTY ? in a forked process

output

Case I: node parent
Parent:  true  From tty:  true
Parent:  true  From tty:  true
TTY:  true  From tty:  true
TTY:  true  From tty:  true

Case II: node parent > asdf
Parent:  true  From tty:  true
Parent:  undefined  From tty:  true
TTY:  true  From tty:  true
TTY:  undefined  From tty:  true

Case III: cat asdf | node parent
Parent:  undefined  From tty:  false
Parent:  true  From tty:  false
TTY:  undefined  From tty:  false
TTY:  true  From tty:  false

Case IV: cat asdf | node parent > asdf
Parent:  undefined  From tty:  false
Parent:  undefined  From tty:  false
TTY:  undefined  From tty:  false
TTY:  undefined  From tty:  false

parent.js

var cp = require('child_process');
var tty = require('tty');
cp.fork('./tty.js');
console.log("Parent: ", process.stdin.isTTY, " From tty: ", tty.isatty(process.stdin));
console.log("Parent: ", process.stdout.isTTY, " From tty: ", tty.isatty(process.stdout));

test.sh

echo "Case I: node parent"
node parent
echo ""

echo "Case II: node parent > asdf"
node parent > asdf
cat asdf
echo ""

echo "Case III: cat asdf | node parent"
cat asdf | node parent
echo ""

echo "Case IV: cat asdf | node parent > asdf"
cat asdf | node parent > asdf
cat asdf

tty.js

var tty = require('tty');
console.log("TTY: ", process.stdin.isTTY, " From tty: ", tty.isatty(process.stdin));
console.log("TTY: ", process.stdout.isTTY, " From tty: ", tty.isatty(process.stdout));