Shell Tail command in Node.js

tail.js

#!/usr/bin/env node

let fs = require('fs');
let path = require('path');

let args = process.argv.slice(2);
//console.log(args);

let parseArgs = (args) => {
  let parsed = {};
  let maxlen = 2;

  let argsStr = args.join(' ');
  
  let file = argsStr.match(/-(-)?f(ile)?(=|[\s])"?(?<file>\S+)"?/);

  if (file && file.groups && file.groups.file) {
    file = file.groups.file;
  }

  if (!file) {
    throw new Error('Argument --file(-f) is required!');
  }

  let lines = argsStr.match(/-(-)?l(ines)?(=|[\s])"?(?<lines>\S+)"?/);

  if (lines && lines.groups && lines.groups.lines) {
    lines = Number(lines.groups.lines);
  } else {
    lines = 10;
  }

  return {
    file: file.trim(),
    lines
  }
}

let file, lines;

try {
  let parsed = parseArgs(args);
  file = parsed.file;
  lines = parsed.lines;
} catch (e) {
  console.log(e.message);
  return 0;
}


//console.log('file >> ', file);
//console.log('lines >> ', lines);

fs.readFile(path.join(__dirname,file), (err, data) => {
  if (err) {
    console.log('Error:' + err.message);
    return 0;
  }

  //console.log('Data: > ', data);
  let out = data.toString().split("\n").slice(-(lines + 1)).join("\n");
  console.log(out);
  return 1;
});