How do I add to the Windows PATH variable using setx? Having weird problems

Run cmd as administrator, then:

setx /M PATH "%PATH%;<your-new-path>"

The /M option sets the variable at SYSTEM scope. The default behaviour is to set it for the USER.

TL;DR

The truncation issue happens because when you echo %PATH% it will show the concatenation of SYSTEM and USER values. So when you add it in your second argument to setx, it will be fitting SYSTEM and USER values inside the USER var. When you echo again, things will be doubled.

Additionally, the /M option requires administrator privilege, so you need to open your terminal with "run as administrator", otherwise setx will complain with "access to registry path is denied".

Last thing to note: You won't see the new value when you echo %PATH% just after setting it this way, you need to close cmd and open again.

If you want to check the actual values stored in registry check this question.

This works perfectly:

for /f "usebackq tokens=2,*" %A in (`reg query HKCU\Environment /v PATH`) do set my_user_path=%Bsetx PATH "C:\Python27;C:\Python27\Scripts;%my_user_path%"

The 1st command gets the USER environment variable 'PATH', into 'my_user_path' variableThe 2nd line prepends the 'C:\Python27;C:\Python27\Scripts;' to the USER environment variable 'PATH'

If someone want to run it in PowerShell it works like below,

Run Powershell as Administrator

Then

setx /M PATH "$Env:PATH;<path to add>"

To verify, open another Powershell and view PATH as below,

$Env:PATH