How to check if a program is run in Bash on Ubuntu on Windows and not just plain Ubuntu?

Question

Pretty straightforward, the usual places to figure out the OS you\'re on seem to be identical to plain Ubuntu on Ubuntu for Windows. For example uname -a is ide

Answer 1

Without me doing anything special, these environment variables seem to be set already:

$ set | grep WSL
IS_WSL='Linux version 4.4.0-18362-Microsoft (Microsoft@Microsoft.com) (gcc version 5.4.0 (GCC) ) #1-Microsoft Mon Mar 18 12:02:00 PST 2019'
WSLENV=
WSL_DISTRO_NAME=Debian

So, something like the following snippet should also work in this case (example of what I used it for myself):

if [ ! -z "$IS_WSL" ]; then
    alias code='/mnt/c/Users/per/AppData/Local/Programs/Microsoft\ VS\ Code/Code.exe'
fi

(Note that technically, -z does not check if the variable is unset, merely that it is empty; in practice, this works well enough in this case. The ! at the beginning is there to negate the check.)