<?php
$filesDir = $files->getFilesDir();
$file = $files->buildFile(function ($fileBuilder) use ($filesDir) {
    $fileBuilder->setPath($filesDir, "tmp/aaa.txt");
});
$file->writeText("hello world", "UTF-8");
$file->appendText("hi world", "UTF-8");
$console->log($file->readText("UTF-8"));
$file->delete();