Is it possible to send data to the the shell of another pseudo-terminal?

Question

This image shows how pseudo-terminals work:

If I have two terminal emulators open, I can send the string "Hello" from the first terminal emulator to the second terminal emulator:

echo "Hello" > /dev/pts/1

When this command is executed, the string "Hello" will travel from the slave side of the second pseudo-terminal to the master side of the second pseudo-terminal and then gets displayed on the second terminal emulator.

Now is it possible to send data in the opposite direction, that is, to send data to the shell instead of the terminal emulator (or the process that the shell is running)?

Answer 1

TIOCSTI works as said in a comment by thrig above: https://stackoverflow.com/a/29615101/2995591

Answer 2

It might not exactly be what you are looking for, but these kind of problems I usually solve by running screen sessions in my terminals.

I do it like this:

• In terminal 1 I start a new screen session called term1 with screen -S term1
  Often when I need this functionality terminal 1 doesn't exist yet. In that case I create the session in a new terminal with xterm -e screen -S term1 & ; disown
  You might be wondering about the & ; disown. This is because I want the shell back after xterm has launched and I don't want xterm to die if the shell where I launched it dies
• I do something similar in the 2nd terminal: screen -S term2 (or create a new terminal by running xterm -e screen -S term2 & ; disown)
• Communication now works as follows:
  • You can send text to the 1st terminal from everywhere (including terminal 2) with a command like:
    screen -S term1 -X stuff 'echo "foo"\n'
    The result would be the same as entering echo "foo" at the 1st terminal and pressing Enter
  • Easier example: to send the input some words but not following it by Enter to terminal 2 you can use screen -S term2 -X stuff 'some words'

Sidenotes:

• If you already had screen sessions named term1 and/or term2 use other names
• If you ran screen -S somename in a already existing terminal note that only the screen session is killed after running exit.
  If you want the whole terminal to stop then use screen -S somename ; exit instead.
  This is not necessary in newly created terminals.

Answer 3

Each proccess has 3 default "file descriptors"

0 is stdin  (standart input)
1 is stdout (standart output)
2 is stderr (standart error output)

You need to find PID of shell process and then you can do following:

echo "test" > /proc/{your_shell_pid}/fd/1

This will print test in the shell process' standart output