p.js

var i = j = 0,a=[];

setInterval(function() {
  process.stdout.clearLine();
  process.stdout.cursorTo(0);

  if(++i>20) i=0;
  for(j=0;j<i;j++) a.push('x');
  for(;j<20;j++)a.push(' ');
  process.stdout.write('['+ a.join('')+ '] ' + i +'/20');
  a=[];

},100);