playing with PATH on Windows

.gitignore

@@ -1,3 +1,5 @@
+*~
+
 # ---> Go
 # Binaries for programs and plugins
 *.exe

winpath/README.md

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+# winpath
+
+An example of getting, setting, and broadcasting PATHs on Windows.
+
+This requires the `unsafe` package to use a syscall with special message poitners to update `PATH` without a reboot.
+It will also build without `unsafe`.
+
+```bash
+go build -tags unsafe -o winpath.exe
+```
+
+```bash
+winpath show
+
+        %USERPROFILE%\AppData\Local\Microsoft\WindowsApps
+        C:\Users\me\AppData\Local\Programs\Microsoft VS Code\bin
+        %USERPROFILE%\go\bin
+        C:\Users\me\AppData\Roaming\npm
+        C:\Users\me\AppData\Local\Keybase\
+```
+
+```bash
+winpath append C:\someplace\special
+
+	Run the following for changes to take affect immediately:
+	PATH %PATH%;C:\someplace\special
+```
+
+```bash
+winpath prepend C:\someplace\special
+
+	Run the following for changes to take affect immediately:
+	PATH C:\someplace\special;%PATH%
+```
+
+```bash
+winpath remove C:\someplace\special
+```
+
+# Special Considerations
+
+Giving away the secret sauce right here:
+
+* `HWND_BROADCAST`
+* `WM_SETTINGCHANGE`
+
+This is essentially the snippet you need to have the HKCU and HKLM Environment registry keys propagated without rebooting:
+
+```go
+	HWND_BROADCAST   := uintptr(0xffff)
+	WM_SETTINGCHANGE := uintptr(0x001A)
+	_, _, err := syscall.
+		NewLazyDLL("user32.dll").
+		NewProc("SendMessageW").
+		Call(HWND_BROADCAST, WM_SETTINGCHANGE, 0, uintptr(unsafe.Pointer(syscall.StringToUTF16Ptr("ENVIRONMENT"))))
+
+```
+
+* `os.Getenv("COMSPEC")`
+* `os.Getenv("SHELL")`
+
+If you check `SHELL` and it isn't empty, then you're probably in MINGW or some such.
+If that's empty but `COMSPEC` isn't, you can be reasonably sure that you're in cmd.exe or Powershell.

winpath/go.mod

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+module git.coolaj86.com\coolaj86\go-examples\winpath
+
+go 1.12
+
+require golang.org/x/sys v0.0.0-20190712062909-fae7ac547cb7

winpath/go.sum

@@ -0,0 +1,2 @@
+golang.org/x/sys v0.0.0-20190712062909-fae7ac547cb7 h1:LepdCS8Gf/MVejFIt8lsiexZATdoGVyp5bcyS+rYoUI=
+golang.org/x/sys v0.0.0-20190712062909-fae7ac547cb7/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=

winpath/winpath.go

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+// +build windows
+
+// We both need to
+//   * use the registry editor directly to avoid possible PATH  truncation
+//     ( https://stackoverflow.com/questions/9546324/adding-directory-to-path-environment-variable-in-windows )
+//     ( https://superuser.com/questions/387619/overcoming-the-1024-character-limit-with-setx )
+//   * explicitly send WM_SETTINGCHANGE
+//     ( https://github.com/golang/go/issues/18680#issuecomment-275582179 )
+//   * also install as a service
+//     ( https://github.com/golang/sys/blob/master/windows/svc/example/install.go )
+package main
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"golang.org/x/sys/windows/registry"
+)
+
+var sendmsg func()
+
+func usage() {
+	fmt.Fprintf(os.Stderr, "Usage: winpath show|append|prepend|remove <path>\n")
+}
+
+func main() {
+	fmt.Println("PATH:", os.Getenv("PATH"))
+	//fpath, err := exec.LookPath("reg")
+	//fmt.Println("LookPath(\"reg\"):", fpath, err)
+
+	shell := os.Getenv("SHELL")
+	if "" == shell {
+		if strings.HasSuffix(os.Getenv("COMSPEC"), "/cmd.exe") {
+			shell = "cmd"
+		}
+	}
+	fmt.Println("SHELL?", shell)
+	fmt.Println("os.PathListSeparator:", string(os.PathListSeparator))
+	// WM_SETTING_CHANGE
+	// https://gist.github.com/microo8/c1b9525efab9bb462adf9d123e855c52
+	// os.Setenv("PATH")
+
+	// TODO --system to add to the system PATH rather than the user PATH
+	if len(os.Args) < 2 {
+		usage()
+		os.Exit(1)
+	}
+	action := os.Args[1]
+
+	paths, err := Paths()
+	if nil != err {
+		fmt.Fprintf(os.Stderr, "%s\n", err)
+		os.Exit(2)
+	}
+
+	if "show" == action {
+		if len(os.Args) > 2 {
+			usage()
+		}
+		fmt.Println()
+		for i := range paths {
+			fmt.Println("\t" + paths[i])
+		}
+		fmt.Println()
+		return
+	}
+
+	if len(os.Args) < 3 {
+		usage()
+		os.Exit(1)
+	}
+
+	pathname := os.Args[2]
+	abspath, err := filepath.Abs(pathname)
+	if nil != err {
+		fmt.Fprintf(os.Stderr, "%s\n", err)
+		os.Exit(2)
+	}
+	if "remove" != action {
+		stat, err := os.Stat(pathname)
+		if nil != err {
+			fmt.Fprintf(os.Stderr, "%s\n", err)
+			os.Exit(2)
+		}
+		if !stat.IsDir() {
+			fmt.Fprintf(os.Stderr, "%q is not a directory (folder)\n", pathname)
+			os.Exit(2)
+		}
+	}
+
+	index := -1
+	for i := range paths {
+		if pathname == paths[i] {
+			index = i
+			break
+		}
+		if abspath == paths[i] {
+			index = i
+			break
+		}
+	}
+
+	switch action {
+	default:
+		usage()
+		os.Exit(1)
+	case "append":
+		if index >= 0 {
+			fmt.Fprintf(os.Stderr, "%q is already in PATH at position %d. Remove it first to re-order.\n", pathname, index)
+			os.Exit(3)
+		}
+		paths = append(paths, pathname)
+		fmt.Println("Run this to cause settings to take affect immediately:")
+		fmt.Println("\tPATH %PATH%;" + pathname)
+	case "prepend":
+		if index >= 0 {
+			fmt.Fprintf(os.Stderr, "%q is already in PATH at position %d. Remove it first to re-order.\n", pathname, index)
+			os.Exit(3)
+		}
+		paths = append([]string{pathname}, paths...)
+		fmt.Println("Run this to cause settings to take affect immediately:")
+		fmt.Println("\tPATH " + pathname + ";%PATH%")
+	case "remove":
+		if index < 0 {
+			fmt.Fprintf(os.Stderr, "%q is NOT in PATH.\n", pathname)
+			os.Exit(3)
+		}
+		oldpaths := paths
+		paths = []string{}
+		for i := range oldpaths {
+			if i != index {
+				paths = append(paths, oldpaths[i])
+			}
+		}
+	}
+
+	k, err := registry.OpenKey(registry.CURRENT_USER, `Environment`, registry.SET_VALUE)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "%s\n", err)
+		os.Exit(4)
+	}
+	defer k.Close()
+	// ";" on Windows
+	err = k.SetStringValue(`Path`, strings.Join(paths, string(os.PathListSeparator)))
+	if nil != err {
+		fmt.Fprintf(os.Stderr, "%s\n", err)
+		os.Exit(4)
+	}
+	err = k.Close()
+	if nil != err {
+		fmt.Fprintf(os.Stderr, "%s\n", err)
+		os.Exit(4)
+
+	}
+
+	err = os.Setenv(`PATH`, strings.Join(paths, string(os.PathListSeparator)))
+	if nil != err {
+		fmt.Fprintf(os.Stderr, "%s\n", err)
+		os.Exit(4)
+	}
+	if nil != sendmsg {
+		fmt.Println("Open a new Terminal for the updated PATH")
+		sendmsg()
+	} else {
+		fmt.Println("You'll need to reboot for setting to take affect")
+	}
+}
+
+func Paths() ([]string, error) {
+	k, err := registry.OpenKey(registry.CURRENT_USER, `Environment`, registry.QUERY_VALUE)
+	if err != nil {
+		return nil, err
+	}
+	defer k.Close()
+
+	// This is case insensitive (PATH, Path, path)
+	s, _, err := k.GetStringValue("Path")
+	if err != nil {
+		return nil, err
+	}
+	// ";" on Windows
+	return strings.Split(s, string(os.PathListSeparator)), nil
+
+	/*
+		shstr := loader()
+		if "" == shstr {
+			shstr = "NO_SHELL_DETECTED"
+		}
+		if "" == s {
+			s = "NO_WINREG_PATH"
+		}
+
+		return fmt.Sprintf("%s\n%s", s, shstr)
+	*/
+}

winpath/winpath_unsafe.go

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+// +build windows,unsafe
+
+package main
+
+import (
+	"os"
+	"fmt"
+	"syscall"
+	"unsafe"
+)
+
+const (
+	HWND_BROADCAST   = uintptr(0xffff)
+	WM_SETTINGCHANGE = uintptr(0x001A)
+)
+
+func init() {
+	sendmsg = func() {
+		//x, y, err := syscall.
+		_, _, err := syscall.
+			NewLazyDLL("user32.dll").
+			NewProc("SendMessageW").
+			Call(HWND_BROADCAST, WM_SETTINGCHANGE, 0, uintptr(unsafe.Pointer(syscall.StringToUTF16Ptr("ENVIRONMENT"))))
+		//fmt.Fprintf(os.Stderr, "%d, %d, %s\n", x, y, err)
+		if nil != err {
+			fmt.Fprintf(os.Stderr, "%s\n", err)
+		}
+	}
+}