I use this command to fill out a form in Drupal 6 (create node):
curl -b cookies.txt -d "title=thetitle&menu%5Blink_title%5D=&menu%5Bparent%5D=primary-links%3A0&menu%5Bweight%5D=0&teaser_include=1&body=content+here&format=1&changed=&form_build_id=form-01fbf44be3dab1ea177d17544bce415c&form_token=f1af1b01946065a34e49fdbde8fcc64b&form_id=story_node_form&log=&comment=2&pathauto_perform_alias=1&field_pidio%5B0%5D%5Bembed%5D=&name=admin&date=&status=1&promote=1&op=Save" http://localhost/subdo/node/add/story
It works without any problem; no messages in the terminal and the node is created in Drupal as expected.
After a while, I use that code again without any modification. But instead of posting a new node, the terminal shows the HTML code of the form. It looks like cURL isn't hitting the "Save" button.