Examples

A custom : command

fn say_hello(arg) {
    smaragd_status("Hello, " + arg + "!");
}
register_command("hello", "say_hello");
register_shortcut("hello", "ctrl+shift+h");

Typing :hello world in the command prompt calls say_hello("world") and shows “Hello, world!” in the status bar. Everything after the command name is passed as a single string argument. Pressing Ctrl+Shift+H runs the same command with an empty argument.

Shelling out to a tool

fn wordcount(arg) {
    let result = smaragd_run_command("wc", ["-w"]);
    smaragd_status("Words: " + result.stdout);
}
register_command("wordcount", "wordcount");

An on_save hook

fn on_save(text) {
    text.trim() + "\n"
}

This runs before every explicit save (:w / Ctrl+S / :wq), in plugin-load order, each hook’s output feeding the next. Return a String to replace the saved text; return anything else (typically nothing) to leave it unchanged. If a hook throws, that plugin’s change is dropped and an error is shown — a broken plugin can never block a save.

Note: on_save only runs on those explicit save actions — not the focus-loss autosave, and not the save-before-switching-documents path.