[Windows] Share environment variables in Windows Subsystem for Linux

Now that you have your fancy WSL up and running, you want to use it and all your environment variables are NOT available (of course).

Luckily there is a workaround, using the WSLENV variable. Unfortunately, it is not a direct 1:1 translation of your existing variables, rather you will need to craft them manually and convert between the two environments before you run a command or switch environment.

For example, to pass your JAVA_HOME correctly to wsl:

set JAVA_HOME=%JAVA_HOME%
set WSLENV=JAVA_HOME/up
wsl
echo $JAVA_HOME

And the magic is behind that last /up flag which says: set the value when invoking WSL from Windows (u) and translate between Windows and Unix paths (p)

WARNING: spaces are NOT escaped
WARNING2: only ONE variable is shared, so you cannot share both JAVA_HOME and PATH for example at the same time