How to extract and save the position information from nav_msgs to a text file

edit

I have a topic published named "cmd_local_waypoints" with two waypoints where the robot to go. I need to extract the X and Y position information from the topic and need to save it to a text file. The terminal response is shown below. You can see two position information available in the topic. I need to save it to a text file

Thanks in advance

header: 
  seq: 2219
  stamp: 
    secs: 17116
    nsecs: 995000000
  frame_id: ''
poses: []
---
header: 
  seq: 2220
  stamp: 
    secs: 17117
    nsecs:  14000000
  frame_id: base_link
poses: 
  - 
    header: 
      seq: 0
      stamp: 
        secs: 17117
        nsecs:  14000000
      frame_id: base_link
    pose: 
      position: 
        x: -2.32830643654e-05
        y: -2.32830643654e-05
        z: -2.32830643654e-05
      orientation: 
        x: 3.4668537268e-310
        y: 3.46685372677e-310
        z: 0.0
        w: 1.0
  - 
    header: 
      seq: 0
      stamp: 
        secs: 17117
        nsecs:  14000000
      frame_id: base_link
    pose: 
      position: 
        x: -2.32830643654e-05
        y: -2.32830643654e-05
        z: -2.32830643654e-05
      orientation: 
        x: 3.46686898944e-310
        y: 3.46688499512e-310
        z: 0.0
        w: 1.0