Goでクリップボード監視をする（Windows Vista以降） ref: http://qiita.com/kurogelee/items/8b39f84b69b63c425a7d

watch_clipboard.go

package main

import (
    "fmt"
    "syscall"
    "unsafe"

    "github.com/AllenDang/w32"
)

func getClipText() (string, error) {
    if w32.OpenClipboard(0) {
        defer w32.CloseClipboard()
        hclip := w32.HGLOBAL(w32.GetClipboardData(w32.CF_UNICODETEXT))
        if hclip == 0 {
            return "", fmt.Errorf("GetClipboardData")
        }

        lpstr := w32.GlobalLock(hclip)
        defer w32.GlobalUnlock(hclip)
        return w32.UTF16PtrToString((*uint16)(lpstr)), nil
    }
    return "", fmt.Errorf("OpenClipboard")
}

func wndProc(hwnd w32.HWND, msg uint32, wParam, lParam uintptr) uintptr {
    if msg == w32.WM_CLIPBOARDUPDATE {
        text, err := getClipText()
        if err != nil {
            fmt.Println("error:", err)
            return 0
        }
        fmt.Println("clipdata:", text)
        return 0
    }
    return w32.DefWindowProc(hwnd, msg, wParam, lParam)
}

func main() {
    className := syscall.StringToUTF16Ptr("for clipboard")
    wndClassEx := w32.WNDCLASSEX{
        ClassName: className,
        WndProc:   syscall.NewCallback(wndProc),
    }
    wndClassEx.Size = uint32(unsafe.Sizeof(wndClassEx))
    w32.RegisterClassEx(&wndClassEx)

    // Message-Only Window
    hwnd := w32.CreateWindowEx(0, className, className, 0, 0, 0, 0, 0, w32.HWND_MESSAGE, 0, 0, nil)
    w32.AddClipboardFormatListener(hwnd)
    defer w32.RemoveClipboardFormatListener(hwnd)

    msg := w32.MSG{}
    for w32.GetMessage(&msg, 0, 0, 0) > 0 {
        w32.DispatchMessage(&msg)
    }
}