Tutorial 1: Hello, Log

Built from a single call already used throughout this wiki (Loader.Printf) — the only thing new here is slowing down to look at just this one piece by itself, as a true first step.

Before anything else — a menu, a spawned vehicle, a whole gamemode — you need to know your own code actually ran at all. The smallest possible way to check that is to print one line somewhere you can go look at it.

The code

Create scripts/OnKey/hello_log.lua:

local KEYVAL = "insert"  -- must be in the first 10 lines

Loader.Printf("[hello_log] the key was pressed!")

Load into a level, then press Insert.

Where the line actually went

Nothing appeared on your screen — that’s expected. Loader.Printf writes to a plain text file next to your game’s .exe, called lua_loader_printf.log, not to the screen. Open that file in any text editor after pressing the key. You should see your line at the very bottom:

[hello_log] the key was pressed!

[Image placeholder — ../img/hellologfile.png] Screenshot of lua_loader_printf.log open in a plain text editor (e.g. Notepad), with the file path visible in the title bar, showing [hello_log] the key was pressed! as the most recent line at the bottom of the file.

Press Insert a few more times, then reopen the file — a new line appears each time. This file only ever contains things a script explicitly asked to print — nothing from the base game leaks into it, unlike the engine’s own shared debug log. That’s why every tutorial from here on uses it: it’s your own, private, always-available window into “what is my script actually doing right now.”

What’s actually happening

Loader.Printf(message) is a global function — available in every script, no setup line needed — that takes one string and appends it as a new line in that log file. That’s the whole mechanism. The "[hello_log] " prefix isn’t required by anything; it’s a convention used throughout this wiki so that when several scripts are all writing to the same file, you can tell at a glance which script wrote which line. Get in the habit now — by Tutorial 4 you’ll have two scripts logging at once.

Try it yourself

• Change the message text and press Insert again — confirm the new text shows up, not the old one, and that the old line is still there above it.
• Add a second Loader.Printf(...) line to the same script, with different text — confirm both lines appear, in order, after just one keypress.
• Try Loader.Printf(42) — a number instead of a string in quotes. Does it work, or does it complain? If it complains, try Loader.Printf(tostring(42)) instead and compare.
• Pick a different key (change "insert" to "home", "end", or another key name) and confirm it still works. This is the same KEYVAL line every OnKey script in this wiki uses.

Where this comes from

• Getting Started: Loader.Printf — why this exists instead of the engine’s own Debug.Printf.
• Glossary: Loader.Printf / KEYVAL

Next: Tutorial 2: Hello, Screen — the same idea, but somewhere you don’t have to alt-tab out of the game to see it.