old_contents: var exec = require ('child_process') .exec;
  
  console.log ('Checking vnStat requirement...');
  
  exec ('vnstat --version', function (err, res, stderr) {
    if (err) { throw err; }
    res.replace (/^vnStat (\d+)\.(\d+) /, function (s, major, minor) {
      if (major >= 1 && minor >= 13) {
        console.log ('vnStat correct');
      } else {
        console.log ('Wrong vnStat version: requires >= v1.13, but v'+ major +'.'+ minor +' installed');
        process.exit (1);
      }
    });
  });
new_contents: var exec = require ('child_process') .exec;
  
  console.log ('Checking vnStat requirement...');
  
  exec ('vnstat --version', function (err, res, stderr) {
    if (err) {
      throw err;
    }
  
    res.replace (/^vnStat (\d+)\.(\d+) /, function (s, major, minor) {
      if (major >= 1 && minor >= 13) {
        console.log ('vnStat correct');
        return;
      }
  
      console.log ('Wrong vnStat version: requires >= v1.13, but v' + major + '.' + minor + ' installed');
      process.exit (1);
    });
  });
  
subject: Clean up preinstall.js