drupal/modules/update/update.settings.inc

<?php
// $Id$

/**
 * @file
 * Code required only for the update status settings form.
 */

/**
 * Form builder for the update settings tab.
 */
function update_settings() {
  $form = array();

  $notify_emails = variable_get('update_notify_emails', array());
  $form['update_notify_emails'] = array(
    '#type' => 'textarea',
    '#title' => t('E-mail addresses to notify when updates are available'),
    '#rows' => 4,
    '#default_value' => implode("\n", $notify_emails),
    '#description' => t('Whenever your site checks for available updates and finds new releases, it can notify a list of users via e-mail. Put each address on a separate line. If blank, no e-mails will be sent.'),
  );

  $form['update_check_frequency'] = array(
    '#type' => 'radios',
    '#title' => t('Check for updates'),
    '#default_value' => variable_get('update_check_frequency', 1),
    '#options' => array(
      '1' => t('Daily'),
      '7' => t('Weekly'),
    ),
    '#description' => t('Select how frequently you want to automatically check for new releases of your currently installed modules and themes.'),
  );

  $form['update_notification_threshold'] = array(
    '#type' => 'radios',
    '#title' => t('Notification threshold'),
    '#default_value' => variable_get('update_notification_threshold', 'all'),
    '#options' => array(
      'all' => t('All newer versions'),
      'security' => t('Only security updates'),
    ),
    '#description' => t('If there are updates available of Drupal core or any of your installed modules and themes, your site will print an error message on the <a href="@status_report">status report</a>, the <a href="@modules_page">modules page</a>, and the <a href="@themes_page">themes page</a>. You can choose to only see these error messages if a security update is available, or to be notified about any newer versions.', array('@status_report' => url('admin/logs/status'), '@modules_page' => url('admin/build/modules'), '@themes_page' => url('admin/build/themes')))
  );

  $form = system_settings_form($form);
  // Custom valiation callback for the email notification setting.
  $form['#validate'][] = 'update_settings_validate';
  // We need to call our own submit callback first, not the one from
  // system_settings_form(), so that we can process and save the emails.
  unset($form['#submit']);

  return $form;
}

/**
 * Validation callback for the settings form.
 *
 * Validates the email addresses and ensures the field is formatted correctly.
 */
function update_settings_validate($form, &$form_state) {
  if (!empty($form_state['values']['update_notify_emails'])) {
    $valid = array();
    $invalid = array();
    foreach (explode("\n", trim($form_state['values']['update_notify_emails'])) as $email) {
      $email = trim($email);
      if (!empty($email)) {
        if (valid_email_address($email)) {
          $valid[] = $email;
        }
        else {
          $invalid[] = $email;
        }
      }
    }
    if (empty($invalid)) {
      $form_state['notify_emails'] = $valid;
    }
    elseif (count($invalid) == 1) {
      form_set_error('update_notify_emails', t('%email is not a valid e-mail address.', array('%email' => reset($invalid))));
    }
    else {
      form_set_error('update_notify_emails', t('%emails are not valid e-mail addresses.', array('%emails' => implode(', ', $invalid))));
    }
  }
}

/**
 * Submit handler for the settings tab.
 */
function update_settings_submit($form, $form_state) {
  $op = $form_state['values']['op'];

  if ($op == t('Reset to defaults')) {
    unset($form_state['notify_emails']);
  }
  else {
    if (empty($form_state['notify_emails'])) {
      variable_del('update_notify_emails');
    }
    else {
      variable_set('update_notify_emails', $form_state['notify_emails']);
    }
    unset($form_state['notify_emails']);
    unset($form_state['values']['update_notify_emails']);
  }
  system_settings_form_submit($form, $form_state);
}