drupal: create the custom term if not exist.

gistfile1.php

<?php
function get_term_tid($term_name, $vocabulary){
  $terms = taxonomy_get_term_by_name($term_name, $vocabulary->machine_name);
  if (empty($terms)) {
    $term = create_term($term_name, $vocabulary);
    return $term->tid;
  } else {
    return reset($terms)->tid;
  }
}

function create_term($term_name, $vocabulary){
  $term = new stdClass();
  $term->vid = $vocabulary->vid;
  $term->name = trim($term_name);
  taxonomy_term_save($term);
  return $term;
}