Create grammar check with pegjs

check

#!/usr/bin/env node
'use strict';

const fs = require('fs');
const parser = require('./grammar.js').parse;

function main() {
  const args = require('process').argv;
  if (args.length != 3) {
    console.error("Only 1 argument needed: file-path")
    return 1;
  }
  const filename = args[2];
  fs.readFile(filename, {encoding: 'utf8'}, function(err, data) {
    if (err) {
      console.log("Error reading file", filename);
      console.error(err);
      return 1;
    }
    try {
      let output = parser(data);
      console.log(output);
    }
    catch (e) {
      console.error(e.message);
    }
  });
}

main();

grammar.peg

page = header description examples eof {"OK"}
header = command nl underline nl nl
description = (descriptor nolowercase any dot nl)+
examples = example (nl example)*
example = example_description nl example_command
example_description = nolowercase any colon nl
example_command = fourspace any nl
command = [a-zA-Z0-9_][-a-zA-Z0-9_ ]*
underline = '='+
any = [a-z ()-,-.={}/_0-9A-Z]*
nolowercase = [^a-z]
descriptor = '> '
fourspace = '    '
dot = .
colon = ':'
nl = [\n]
eof = !.

Do chmod +x grammar and compile your grammar like: pegjs grammar.peg grammar.js and after that you can deploy like: grammar FILENAME (where FILENAME is the location of the file to be checked).