How to capture global keystrokes with PowerShell?

Question

Can Powershell listen for and capture key presses?

Is it possible to write a PowerShell script that, like AutoHotkey, sits in tray and waits until you press a predef

Answer 1

Not in PowerShell directly maybe, but as you can run pretty much any C# code, here is a basic working example based on an excellent solution by Peter Hinchley:

Add-Type -TypeDefinition '
using System;
using System.IO;
using System.Diagnostics;
using System.Runtime.InteropServices;
using System.Windows.Forms;

namespace KeyLogger {
  public static class Program {
    private const int WH_KEYBOARD_LL = 13;
    private const int WM_KEYDOWN = 0x0100;

    private static HookProc hookProc = HookCallback;
    private static IntPtr hookId = IntPtr.Zero;
    private static int keyCode = 0;

    [DllImport("user32.dll")]
    private static extern IntPtr CallNextHookEx(IntPtr hhk, int nCode, IntPtr wParam, IntPtr lParam);

    [DllImport("user32.dll")]
    private static extern bool UnhookWindowsHookEx(IntPtr hhk);

    [DllImport("user32.dll")]
    private static extern IntPtr SetWindowsHookEx(int idHook, HookProc lpfn, IntPtr hMod, uint dwThreadId);

    [DllImport("kernel32.dll")]
    private static extern IntPtr GetModuleHandle(string lpModuleName);

    public static int WaitForKey() {
      hookId = SetHook(hookProc);
      Application.Run();
      UnhookWindowsHookEx(hookId);
      return keyCode;
    }

    private static IntPtr SetHook(HookProc hookProc) {
      IntPtr moduleHandle = GetModuleHandle(Process.GetCurrentProcess().MainModule.ModuleName);
      return SetWindowsHookEx(WH_KEYBOARD_LL, hookProc, moduleHandle, 0);
    }

    private delegate IntPtr HookProc(int nCode, IntPtr wParam, IntPtr lParam);

    private static IntPtr HookCallback(int nCode, IntPtr wParam, IntPtr lParam) {
      if (nCode >= 0 && wParam == (IntPtr)WM_KEYDOWN) {
        keyCode = Marshal.ReadInt32(lParam);
        Application.Exit();
      }
      return CallNextHookEx(hookId, nCode, wParam, lParam);
    }
  }
}
' -ReferencedAssemblies System.Windows.Forms

while ($true) {
    $key = [System.Windows.Forms.Keys][KeyLogger.Program]::WaitForKey()
    if ($key -eq "X") {
        Write-Host "Do something now."
    }
}

Version 2

(using a callback):

Add-Type -TypeDefinition '
  using System;
  using System.IO;
  using System.Diagnostics;
  using System.Runtime.InteropServices;
  using System.Windows.Forms;

  namespace PowerShell {
    public static class KeyLogger {
      private const int WH_KEYBOARD_LL = 13;
      private const int WM_KEYDOWN = 0x0100;

      private delegate IntPtr HookProc(int nCode, IntPtr wParam, IntPtr lParam);

      private static Action keyCallback;
      private static IntPtr hookId = IntPtr.Zero;

      [DllImport("user32.dll")]
      private static extern IntPtr CallNextHookEx(IntPtr hhk, int nCode, IntPtr wParam, IntPtr lParam);

      [DllImport("user32.dll")]
      private static extern bool UnhookWindowsHookEx(IntPtr hhk);

      [DllImport("user32.dll")]
      private static extern IntPtr SetWindowsHookEx(int idHook, HookProc lpfn, IntPtr hMod, uint dwThreadId);

      [DllImport("kernel32.dll")]
      private static extern IntPtr GetModuleHandle(string lpModuleName);

      public static void Run(Action callback) {
        keyCallback = callback;
        hookId = SetHook();
        Application.Run();
        UnhookWindowsHookEx(hookId);
      }

      private static IntPtr SetHook() {
        IntPtr moduleHandle = GetModuleHandle(Process.GetCurrentProcess().MainModule.ModuleName);
        return SetWindowsHookEx(WH_KEYBOARD_LL, HookCallback, moduleHandle, 0);
      }

      private static IntPtr HookCallback(int nCode, IntPtr wParam, IntPtr lParam) {
        if (nCode >= 0 && wParam == (IntPtr)WM_KEYDOWN) {
          var key = (Keys)Marshal.ReadInt32(lParam);
          keyCallback(key);
        }
        return CallNextHookEx(hookId, nCode, wParam, lParam);
      }
    }
  }
' -ReferencedAssemblies System.Windows.Forms

[PowerShell.KeyLogger]::Run({
  param($key)
  if ($key -eq "X") {
    Write-Host "Do something now."
  }
})