Golang: Write a message to any console's input on POSIX.

terminal_darwin.go

//go:build darwin

package main

import (
	"fmt"
	"path/filepath"

	"golang.org/x/sys/unix"
)

// GetTerm returns TTY device of the process with PID `pid`.
func GetTerm(pid int) (string, error) {
	kProc, err := unix.SysctlKinfoProc("kern.proc.pid", int(pid))
	if err != nil {
		return "", fmt.Errorf("Get terminal for PID %v: Get kernel process info: %w", pid, err)
	}
	termMap, err := getTerminalMap()
	if err != nil {
		return "", fmt.Errorf("Get terminal for PID %v: %w", pid, err)
	}
	term, ok := termMap[kProc.Eproc.Tdev]
	if !ok {
		return "", fmt.Errorf("Get terminal for PID %v: Terminal not found", pid)
	}
	return term, nil
}

// getTerminalMap returns mapping between 'st_rdev' and TTY device.
func getTerminalMap() (map[int32]string, error) {
	out := make(map[int32]string)

	termFiles, err := filepath.Glob("/dev/tty*")
	if err != nil {
		return nil, fmt.Errorf("Get terminal map: List TTY devices: %w", err)
	}
	for _, termFile := range termFiles {
		stat := unix.Stat_t{}
		if err := unix.Stat(termFile, &stat); err == nil {
			out[stat.Rdev] = termFile
		}
	}

	return out, nil
}

terminal_posix.go

//go:build !darwin && !windows

package main

import (
	"fmt"

	"github.com/shirou/gopsutil/v4/process"
)

// GetTerm returns TTY device of the process with PID `pid`.
func GetTerm(pid int) (string, error) {
	proc, err := process.NewProcess(int32(pid))
	if err != nil {
		return "", fmt.Errorf("Get terminal of process with PID %v: Create process object: %w", pid, err)
	}
	term, err := proc.Terminal()
	if err != nil {
		return "", fmt.Errorf("Get terminal of process with PID %v: %w", pid, err)
	}
	if term == "" {
		return "", fmt.Errorf("Get terminal of process with PID %v: Terminal not found", pid)
	}
	return "/dev" + term, nil
}

write_to_stdin_posix.go

//go:build !windows

// Used in https://github.com/SCP002/terminator.
// For Windows, see: https://gist.github.com/SCP002/1b7fd91a519a2dc60fc5b179f90472b6.

package main

import (
	"fmt"
	"os"

	"golang.org/x/sys/unix"
)

func main() {
	var pid int
	fmt.Print("PID: ")
	fmt.Scanln(&pid)
	err := Write(pid, "Hello, World!\n")
	if err != nil {
		panic(err)
	}
}

// Write writes a `msg` message to the console process with PID `pid`.
//
// Requires root privilegies (e.g. run as sudo).
func Write(pid int, msg string) error {
	term, err := GetTerm(pid)
	if err != nil {
		return fmt.Errorf("Write message to stdin of the process with PID %v: %w", pid, err)
	}
	file, err := os.OpenFile(term, os.O_WRONLY, 0644)
	if err != nil {
		return fmt.Errorf("Write message to stdin of the process with PID %v: %w", pid, err)
	}
	defer file.Close()
	for _, char := range msg {
		if err = unix.IoctlSetPointerInt(int(file.Fd()), unix.TIOCSTI, int(char)); err != nil {
			return fmt.Errorf("Write message to stdin of the process with PID %v: %w", pid, err)
		}
	}
	return nil
}