crontabEditor.js

const path = require("path");

const exec = (command, options = {}) =>
  require("child_process").execSync(command, { encoding: "utf-8", ...options });

const crontabRead = () => exec("crontab -l").trim();
const crontabWrite = (str) => exec(`echo "${str}" | crontab`);

function parseCrontab() {
  return crontabRead()
    .split("\n")
    .map((content) => ({
      content,
      name: content.match(/#@(.+)@$/)?.[1] || null,
    }));
}

const crontabEditor = (root) => {
  function remove(name) {
    const newCrontab = parseCrontab()
      .filter((l) => l.name !== name)
      .map((a) => a.content)
      .join("\n");
    crontabWrite(newCrontab);
  }

  function write(obj) {
    const toWriteByName = {};

    for (let name in obj) {
      const { when, file, which = "node", log = null } = obj[name];
      toWriteByName[name] =
        [
          when.join(" "),
          "export NODE_PATH=$(npm root --quiet --location=global) &&",
          `$(which ${which})`,
          path.resolve(root + "/" + file),
          log ? `>> ${path.resolve(root + "/" + log)} 2>&1` : null,
        ]
          .filter(Boolean)
          .join(" ") + ` #@${name}@`;
    }

    const replaced = parseCrontab().map(({ content, name }) => {
      if (name in toWriteByName) {
        content = toWriteByName[name];
        delete toWriteByName[name];
      }
      return content;
    });

    crontabWrite(replaced.concat(Object.values(toWriteByName)).join("\n"));
  }

  return { write, remove };
};

/* USAGE:
  
  crontabEditor(__dirname).write({      // set root
    'run': {                            // name of cronjob; overwrites if exists
      when: ['*', '*', '*', '*', '*'],  // minute, hour, ...
      file: 'run.js',                   // file to be executed, relative path
      which: 'node',                    // execution environment; optional, default is node
      log: '.logs/run',                 // cronjob log file; optional
    }
  })


*/