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

Question

I want to modify the Windows PATH variable using setx. The following works at least 50% of the time on Windows 8:

setx PATH %PATH%;C:\Python27\;C:\Python27\Scripts\

If it gives the error "the default argument can only be used 2 times", then the following works some of the time:

setx PATH "%PATH%;C:\Python27\;C:\Python27\Scripts\"

The difference is that we wrapped the second argument in quotes. I believe the quotes are necessary when %PATH% expands to include spaces.

However, I have encountered some weird problems on Windows 7. On one particular Windows 7 machine, I had this problem:

echo %PATH%

It prints:

C:\Foo\;C:\Bar\;[...lots of stuff...]C:\Baz\

Then I do this:

setx PATH "%PATH%;C:\Quux\"

Then it says "Error: Truncated at 1,024 characters." Now let's check what PATH contains:

echo %PATH%

It prints:

C:\Foo\;C:\Foo\;C:\Bar\;C:\Bar\;[...lots of stuff, now duplicated...]C:\B

...and it is cut off at 1,024 characters. It ran over because of the duplicates. Also interesting: The value of PATH changes despite the fact that setx raised an error and did not say "Success".

I was able to repeat this strange behavior several times (luckily I had saved the original contents of PATH).

At the moment, the only surefire way I know to append to the PATH is the following:

1. echo the PATH.

2. Copy the contents of PATH into a text file and manually add ;C:\Python27\;C:\Python27\Scripts\ to the end of the PATH.

3. Copy the whole thing out of the text file.

4. setx PATH "<paste the string here>"

That process works every single time on both Windows 7 and Windows 8.

I should really be able to do this in one command. What am I doing wrong?

Thank you.

Answer 1

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.