check used linux port in range [x,y)

gistfile1.txt

var child_process = require('child_process');
module.exports = function check_linux_port ( port_range, done ) {
    
  var check = child_process.exec('netstat -tln');

  var res   = '';
  check.stdout.on('data',function(chuck) {
    res+= chuck;
  });
  check.on('exit',function(code) {
    if( code == 0 ){
      res = res.split('\n').slice('1');
      res = res.map(function( line ) {
        var host_port = line.match(/(\d+\.\d+\.\d+\.\d+)\:(\d+)/);
        if( host_port ){
          return host_port[2];
        }
      }).filter(function( port ) {
        if( port ){
          port = +port;
          return port >= port_range[0] && port < port_range[1];
        }
      }).sort();
      done( null, res );
    } else {
      done(code);
    }
  });
}