Why is %appdata% and other variable not visible in window's gui

I have searched f开发者_JAVA百科or hours trying to find a reason why certain environment variables are visible in control-panel>system>advance-system-settings>environment-variables. Where are the other variables set and why are they not visible here?

---

Windows stores the location of per-user special folders under the following Registry key:

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\User Shell Folders

The common special folders are specified in the same path under HKEY_LOCAL_MACHINE instead:

HKEY_LOCAL MACHINE\Software\Microsoft\Windows\CurrentVersion\Explorer\User Shell Folders

As for why they're not exposed in the GUI like other user variables, I can only speculate. But my guess is that it's because they're not really intended to be changed by the user. The paths are determined by the system, and are intended for internal use by applications.

---

The variables that are shown in the GUI dialog are the ones that the user can modify.

Others like APPDATA have values that are determined by the system and so Windows doesn't show them in the dialog that allows you to edit them.

---

For the complete list of Windows environment variables including hidden ones take a look at Environment Variables Wiki: System variables, Hidden variables.

Hope that helps.