is-wsl

#!/usr/bin/env bash
set -euo pipefail

#- is-wsl 1.0
## Usage: is-wsl
## Test if running under Windows Subsystem for Linux.

uname | grep -q -i "linux" || exit 1

# https://stackoverflow.com/a/57836260/465684
[[ -z "${IS_WSL:-}" ]] || {
    >&2 echo "$(date +"%H:%M:%S")" "[INFO] Assuming we're running inside WSL because IS_WSL=${IS_WSL}."
    exit 0
}

# https://patrickwu.space/wslconf/
[[ ! -e /proc/sys/fs/binfmt_misc/WSLInterop ]] || {
    >&2 echo "$(date +"%H:%M:%S")" \
        "[INFO] Assuming we're running inside WSL because /proc/sys/fs/binfmt_misc/WSLInterop was found."
    exit 0
}

# https://github.com/Microsoft/WSL/issues/423#issuecomment-221627364
if [[ -e /proc/version ]]; then
    ! cat /proc/version | grep -q -i "Microsoft\|WSL" || {
        >&2 cat /proc/version | grep -i "Microsoft\|WSL"
        >&2 echo "$(date +"%H:%M:%S")" \
            "[INFO] Assuming we're running inside WSL because /proc/version matches Microsoft or WSL."
        exit 0
    }
fi

# https://github.com/Microsoft/WSL/issues/423#issuecomment-221627364
if [[ -e /proc/sys/kernel/osrelease ]]; then
    ! cat /proc/sys/kernel/osrelease | grep -q -i "Microsoft\|WSL" || {
        >&2 cat /proc/sys/kernel/osrelease | grep -i "Microsoft\|WSL"
        >&2 echo "$(date +"%H:%M:%S")" \
            "[INFO] Assuming we're running inside WSL because /proc/sys/kernel/osrelease matches Microsoft or WSL."
        exit 0
    }
fi

! command -v explorer.exe 2>/dev/null >&2 || {
    >&2 echo "$(date +"%H:%M:%S")" "[INFO] Assuming we're running inside WSL because explorer.exe command was found."
    exit 0
}

>&2 echo "$(date +"%H:%M:%S")" "[INFO] Assuming we're not running inside WSL."
exit 1