The Drupal API is very useful, but it cannot be used easily via the command line.

This code allows a PHP shell script to masquerade as a normal request so the Drupal API loads and can be used correctly.

#!/usr/bin/php -q
<?php
 
// set some server variables so Drupal doesn't freak out
$_SERVER['SCRIPT_NAME'] = '/script.php';
$_SERVER['SCRIPT_FILENAME'] = '/script.php';
$_SERVER['HTTP_HOST'] = 'example.com';
$_SERVER['REMOTE_ADDR'] = '127.0.0.1';
$_SERVER['REQUEST_METHOD'] = 'POST';
 
// act as the first user
global $user;
$user->uid = 1;
 
// change to the Drupal directory
chdir('/path/to/drupal');
 
// Drupal bootstrap throws some errors when run via command line
//  so we tone down error reporting temporarily
error_reporting(E_ERROR | E_PARSE);
 
// run the initial Drupal bootstrap process
require_once('includes/bootstrap.inc');
drupal_bootstrap(DRUPAL_BOOTSTRAP_FULL);
 
// restore error reporting to its normal setting
error_reporting(E_ALL);

You can create a shell script file for this code.