Disclaimer: As the title implies, this is about shell scripting on your Steam Deck. The guide won't teach you how to do that part, it assumes you already have ideas in mind about what scripts you'd want to write. Stopping the usage of Syncthing was what I wanted to do with it, but you can do whatever you like.
Background (you can skip this part)
If you're an avid gamer who picked up a Steam Deck and now you're splitting your time between it and a more traditional gaming computer (or in my case, several other gaming systems as well), you may come across a situation where at some point you want to start doing more advanced things on your Steam Deck - which may mean "how do I get files onto or off of this thing".