Accessing existing Windows environment variables from WSL

Question

I would like to access existing Windows environment variables such as USERPROFILE from withing the WSL bash prompt. There is information from Microsoft on the use of WSLENV here, and I have tried to work with this:

I added WSLENV as a new System variable within the usual Windows "Environment Variables" control panel, setting it to USERPROFILE/u. I then open Ubuntu from the taskbar, and type:

$ echo $USERPROFILE

...but nothing is returned.

Answer 1

Improved Gábor's answer, since as I've discovered it had a small bug, variables obtained that way contain invisible carriage return character, that could cause unexpected issues latter. Here is Example:

$ cd /mnt/c/
$ mkdir Windows_NT
$ tmpvar=`/mnt/c/Windows/System32/cmd.exe /C "echo %OS%"`
$ echo $tmpvar
Windows_NT

All seems to be ok, but no:

$ cd $tmpvar
: No such file or directory

This is because tmpvar variable contains additional carriage return character (aka ^M or \r) at the end. We can check this via ls command:

$ ls -ld $tmpvar
ls: cannot access 'Windows_NT'$'\r': No such file or directory

In order to remove that character, output could be be additionally processed with sed or tr:

tmpvar=$(cmd.exe /C echo %OS%|sed $'s/\r$//')

or

tmpvar=$(cmd.exe /C echo %OS%|tr -d '\r')

I've also simplified command a bit. Path /mnt/c/Windows/System32 is already included in $PATH WSL variable by default in recent Windows 10 updates, so just cmd.exe should work.

Now, ls and cd commands work without errors:

$ ls -ld $tmpvar
drwxrwxrwx 1 ubuntu ubuntu 512 Feb 12 05:38 Windows_NT
$ cd $tmpvar
$ pwd
/mnt/c/Windows_NT

pwd command confirms that current directory is correct.