save portion of node

gistfile1.txt

<?php
  $entity = node_load(33);
  
  echo "on load: {$entity->field_test1[LANGUAGE_NONE][0]['value']}<br/>";
  $entity->field_test1[LANGUAGE_NONE][0]['value']='test'.rand(10,100);
  echo "before save: {$entity->field_test1[LANGUAGE_NONE][0]['value']}<br/>";
  
  $entity2=new stdClass;
  $entity2->nid=$entity->nid;
  $entity2->vid=$entity->vid;
  $entity2->type=$entity->type;
  $entity2->field_annonce=$entity->field_annonce;
  
  field_attach_update('node',$entity2);

  $entity = node_load(33);
  echo "after save: {$entity->field_test1[LANGUAGE_NONE][0]['value']}<br/>";
?>