datelock.js

#!/usr/bin/env node
// A simple script that checks for the existence of a "datelock" file. If one
// exists, either returns 1 (error) or 0 (success). I use this to periodically
// update files when a shell starts.
//
// Example usage:
//    // Creates or overwrites a "datelock" file at LOCK_PATH.
//    LOCK_PATH=$HOME/.datelock ./datelock.js write
//    // Checks for a valid lock file at LOCK_PATH, returns 0 or 1.
//    LOCK_PATH=$HOME/.datelock ./datelock.js
//
// Checking a lockfile will return 1 (error) in the following situations:
//    1. The datetime in the lockfile is less than the current datetime.
//    2. The "datelock" file does not exist.
//    3. A system error occurs when reading the LOCK_PATH file (e.g. permission error)

const fs = require("fs");
const now = new Date();

const lockPath = process.env.LOCK_PATH;
if (lockPath === "" || lockPath === undefined) {
  console.log("Usage: LOCK_PATH=<PATH> datelock.js");
  process.exit(1);
}

(async () => {
  try {
    if (process.argv.length > 2 && process.argv[2] == "clear") {
      const file = await fs.promises.rm(lockPath);
      return;
    }

    if (process.argv.length > 2 && process.argv[2] == "write") {
      const file = await fs.promises.open(lockPath, 'w+');
      let tomorrow = now;
      tomorrow.setDate(now.getDate() + 1);
      await file.write(tomorrow.toISOString());
      return;
    }

    const data = await fs.promises.readFile(lockPath, 'utf8');
    const lockDate = Date.parse(data);
    if (isNaN(lockDate) || lockDate < now) {
      process.exit(1);
    }
  } catch (_) {
    process.exit(1);
  }
})();