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 identical to a native GNU/Linux install and /etc/os-version is identical to a Ubuntu Trusty Tahr install.

The only thing I can think of is to check if /mnt/c/Windows exists, but I'm not sure if that's a foolproof idea.

Answer 1

The following works in bash on Windows 10, macOS, and Linux:

#!/bin/bash
set -e
if grep -qEi "(Microsoft|WSL)" /proc/version &> /dev/null ; then
    echo "Windows 10 Bash"
else
    echo "Anything else"
fi

You need to check for both "Microsoft" and "WSL" per this comment by Ben Hillis, WSL Developer:

For the time being this is probably the best way to do it. I can't promise that we'll never change the content of these ProcFs files, but I think it's unlikely we'll change it to something that doesn't contain "Microsoft" or "WSL".

/proc/sys/kernel/osrelease
/proc/version

And case shall be ignored for grep. In WSL2, /proc/version gives lowercased microsoft.