moving a simple object

edit

Your code always publishes the same pos:

  geometry_msgs::PoseStamped msg;

msg contains default values( all zeros, false for bool )

  msg.pose.position.x += 2;

msg.pose.position.x is now (always) 0+2, i. e. 2.!! It does not increment (I guess that'd be your intention).

If you wish to do that define msg in global space, initialize at beginning of main and than increment in your loop like this:

#include <ros/ros.h>
#include "geometry_msgs/PoseStamped.h"
#include "geometry_msgs/Pose.h"
// publisher handles
ros::Publisher goal_pub;
geometry_msgs::PoseStamped msg;

void publish_goal()
{ 
  msg.pose.position.x += 2; 

  goal_pub.publish(msg);
}

int main(int argc, char** argv) 
{

  msg.header.frame_id = "base_link";
  msg.pose.position.x = 2; 
  msg.pose.position.y = 20; 
  msg.pose.position.z = 50;   
  msg.pose.orientation.w = 0; 
  msg.pose.orientation.x = -2.0; 
  msg.pose.orientation.y = 0; 
  msg.pose.orientation.z = 0;  

    ros::init(argc, argv, "move_sphere");
    ros::NodeHandle nh;
    ros::Rate loop_rate(100);
    goal_pub = nh.advertise<geometry_msgs::PoseStamped>("pose", 1);
    while (ros::ok()) 
    {
      publish_goal();
      ros::spinOnce();
      loop_rate.sleep();
    }
}