mike_cesara: Only pointed out, that games will be still downloaded even if you forget changing OS variable.
To go a little more in depth about this, I think it's fair to point out that 'your' method works in some particular cases where 'mine' doesn't.
I'm referring to what we were discussing with pedrovay2003, i.e. games that aren't listed as supporting Linux (or macOS, for that matter) in the store, but they nonetheless have a Linux depot. Sometimes the
app_update command works fine with those games, but sometimes it doesn't, and steamCMD gives me an error message about how I don't have a license for that platform, or something along those lines. In those cases,
a few times the
download_depot does indeed work, but not always. I don't know what could make the difference, there's something that's escaping me about the way the Steam depot and license systems work, no doubt.
So yeah, if you're new to steamCMD, you're probably better off downloading your games like mike_cesara said, as you'll have a higher success rate. When you're eventually fed up about guessing which game corresponds to which game_id, then you'll come to the enlightened path of
app_update. :P