Windows – Avoid alphabetical reading of Windows environment variables

environment-variableswindowswindows 10

Normally, if I define one User Windows 10 environment variable (var 1) in terms of another (var 2), var 2 should precede var 1 in alphabetical order for it to work.
This is identified here, e.g.

For instance, in the window

enter image description here

this

APYTHONDIR  ->  C:\Users\user1\myprogs
PATH  ->  %APYTHONDIR%

works, but this

PYTHONDIR  ->  C:\Users\user1\myprogs
PATH  ->  %PYTHONDIR%

does not.

Is there any way of avoiding it?
Working around it?

I mean to get a solution that functionally works the same as if the variables were defined via registry (or Control Panel).

I can always use naming to ensure "nested" definitions follow alphabetical order.
This is not what I want.

I thought about setting them in the desired order in a startup batch file (autoexec.nt, or whatever is current).
I am not sure if this would work for any application requiring the environment variables.
E.g., octave symbolic integration needing to find python somewhere in the PATH, with the directory in the PATH being added in this way.

EDIT As per the answers by harrymc and myself, and following discussion, this is what I tried:

  1. Creating a file set_env_vars.bat in an arbitrary directory, and set a shortcut to it in %USERPROFILE%\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup.

  2. Adding a line set /P PTEST=Enter value for PTEST in set_env_vars.bat to make sure the file is being read during logon.

  3. Logging off and on. I verified that set_env_vars.bat is read.

Then, I added lines

set ZTEST_DIR=C:\ztest
set YTEST_DIR=%ZTEST_DIR%;C:\ytest

to set_env_vars.bat.
Plus log off / log on.
This didn't give me vars ZTEST_DIR and YTEST_DIR in my environment.

Then, I replaced those with lines

setx ZTEST_DIR C:\ztest
set /P WAITING_DUMMY=Enter value for WAITING_DUMMY   
setx YTEST_DIR %ZTEST_DIR%;C:\ytest

in set_env_vars.bat.
(The second line to try giving time to the system to set the first var).
Plus log off / log on.
This gave me vars 

YTEST_DIR=;C:\ytest
ZTEST_DIR=C:\ztest

in my environment.

Best Answer

If you do set "a=x%b%y", then a is defined exactly like that, and %b% will only be expanded when required. This is why alphabetical order has no importance. Variables are substituted when their value is required, and PATH is an example of a value that is immediately required.

To automate setting environment variables, put the SET commands in a batch file (.bat) and copy the file to the Startup folder.

Your personal startup folder should be C:\Users\<user name>\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup, while the All Users startup folder should be C:\ProgramData\Microsoft\Windows\Start Menu\Programs\Startup.

Question: What am I doing below that is different than what you do? You could show us a similar screenshot if you are getting different results.

enter image description here

As regarding the example you have posted, the results are as expected. You have used the setx command, which sets environment variables for the user in the registry, but not in the local environment. You would need to start a new Command Prompt from the desktop to benefit from that variable.

The important point here is that setx works on the registry, but that does not cause the local environment to be re-evaluated. The environment is built only once, when a process is launched, then stays the same all through execution (unless modified locally by the process itself). Any child started by a parent process will inherit its parent's environment, so no reference is made in that case to the registry.

The demo below demonstrates the problem: The variable is set in the above Command Prompt, but doesn't have a local value. The lower Command Prompt is then started from the desktop, and it does have that value.

enter image description here

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