Editing Windows PATH with AutoHotKey

SysEnv.ahk

#SingleInstance, Force
#NoEnv ; somewhat ironic...
	
	; this won't work in vista/7 if it's not run as an administrator.
	; i'm too lazy to request it manually so the easiest way is to 
	; compile this script, and then under Compatibility tab in the 
	; compiled exe's Properties select "Run as Administrator"
	
	RegRead, P, HKLM, SYSTEM\CurrentControlSet\Control\Session Manager\Environment, PATH
	
	Gui, +Delimiter`;
	
	width := 400
	Gui, Add, Text, w%width%, Double Click an entry to modify it. Click Add to make a new entry and Delete to remove the selected entry.
	Gui, Add, ListBox, vSysPath w%width% r8 +0x100 gEditEntry AltSubmit, %P%
	Gui, Font, s12
	Gui, Add, Button, gNew    w70 section  , New
	Gui, Add, Button, gDelete w70 ys xs+74 , Delete
	Gui, Add, Button, gExit   w70 ys xs+330, Cancel
	Gui, Add, Button, gSubmit w70 ys xp-74, Submit
	Gui, Show, , SysEnv -- Change System Environment Variable
return

EditEntry:
	if (a_guievent == "DoubleClick" && a_eventinfo) {
		Gui +OwnDialogs
		RegExMatch(P, "P)^(?:(?<E>[^;]*)(?:;|$)){" a_eventinfo "}", _)
		_En := IB( "Edit PATH entry", substr(P, _PosE, _LenE))
		if (ErrorLevel == 0)
		{
			if (InStr(FileExist(ExpEnv(_En)),"D"))
			{
				rP := substr(P, 1, _PosE-1) _En (_PosE+_LenE+1 < strlen(P) ? ";" substr(P, _PosE+_LenE+1) : "")
				P := rP
				GuiControl, , SysPath, `;%P%
			}
			else
				MsgBox, , SysEnv, Path is not a directory.
		}
	}
return

New:
	add := IB( "Add PATH entry" )
	if (instr(fileexist(ExpEnv(add)),"D")) {
		P .= (strlen(P) > 0 ? ";" : "") add
		GuiControl, , SysPath, `;%P%
	}
return

Delete:
	GuiControlGet, entry, , SysPath
	if (entry) {
		Gui, +OwnDialogs
		MsgBox, 4, SysEnv -- Confirm, Remove entry #%entry% from PATH?
		IfMsgBox Yes
		{
			RegExMatch(P, "P)^(?:(?<E>[^;]*)(?:;|$)){" entry "}", _)
			P := SubStr(P, 1, max(_PosE-2,0)) (_PosE+_LenE+1 < strlen(P) ? ";" substr(P, _PosE+_LenE+1) : "")
			GuiControl, , SysPath, `;%P%
		}
	}
return

Submit:
	Gui, +OwnDialogs
	MsgBox, 1, SysEnv -- Save Changes, Change system PATH to:`n`n%P%
	IfMsgBox, OK
	{
		RegWrite, REG_EXPAND_SZ, HKLM, SYSTEM\CurrentControlSet\Control\Session Manager\Environment, PATH, %P%
		If !ErrorLevel
                {
                        ;WM_SETTINGCHANGE = 0x1A
                        ;See HWND_BROADCAST in
                        ;http://www.autohotkey.com/docs/commands/PostMessage.htm
                        SendMessage, 0x1A,0,"Environment",, ahk_id 0xFFFF
                        MsgBox, 0, SysEnv -- Success!, Modifying the PATH variable was successful!
                }
		Else
			MsgBox,  , SysEnv, Error has occurred and new PATH variable was not saved.
	}
	Else
		MsgBox, , SysEnv -- Cancelled, Exiting now.

Exit:
GuiClose:
GuiEscape:
GuiEsc:
ExitApp

IB( prompt, default="" ) {
	InputBox, out, SysEnv -- %prompt%, %prompt%:, , , , , , , , %default%
	return out
}

max( a, b ) {
	return a > b ? a : b
}

ExpEnv(str) { 
	; by Lexikos: http://www.autohotkey.com/forum/viewtopic.php?p=327849#327849
	if sz:=DllCall("ExpandEnvironmentStrings", "uint", &str, "uint", 0, "uint", 0)
	{
		VarSetCapacity(dst, A_IsUnicode ? sz*2:sz)
		if DllCall("ExpandEnvironmentStrings", "uint", &str, "str", dst, "uint", sz)
			return dst
	}
	return ""
}