app.js

  var tail_start = function(active, search) {
    var tail_opts = ["-f", "-n", 250, logs[active]];
    
    if (search) {
      processes[sessionId].active_log = active; 
      
      processes[sessionId].grep = spawn("grep", [search]);
      processes[sessionId].grep.stdout.setEncoding('utf8');
      processes[sessionId].grep.stdout.on("data", function(data) {
        console.log("grep STDOUT received data");
      });
      
      processes[sessionId].tail = spawn("tail", tail_opts);
      processes[sessionId].tail.stdout.setEncoding('utf8');
      processes[sessionId].tail.stdout.on("data", function(data) {
        console.log("tail STDOUT received data");
        processes[sessionId].grep.stdin.write(data);
      });

      processes[sessionId].tail.on("exit", function(data) {
        processes[sessionId].grep.stdin.end();
      });

      return;
    }

    processes[sessionId].tail = spawn("tail", tail_opts);
    processes[sessionId].tail.stdout.setEncoding('utf8');
    processes[sessionId].tail.stdout.on("data", emit_data);
  }

  var tail_stop = function() {
    if (processes[sessionId].tail !== null) processes[sessionId].tail.kill();
  }