how to change the value of the form in the preprocess functions or get the value of the function preprocess I need to get the value of preprocess function and write it in the form #default_value, while my form is a variable that preprocess functions
I create custom module

&lt;?php
/**
 * Реализация template_preprocess_comment()
 **/
function comment_email_form_preprocess_comment(&amp;$variables){
    $variables['content']['email_form']['email']['#default_value'] = 'New value!';
    $variables['content']['email_form'] = show(drupal_get_form('comment_email_form'));
    dsm($variables);
}
/**
 * Создаем форму, которая будет хранить данные email адресов бригад и отправлять письмо.
 **/
function comment_email_form($form, &amp;$form_state){
$query = db_select('comment', 'c')
    -&gt;fields('c', array('cid', 'nid'));
$result = $query-&gt;execute();
$comments = array();
foreach($result as $value){
    $comments[$value-&gt;cid] = comment_load($value-&gt;cid);
 }
  $form['email'] = array(
    '#type' =&gt; 'textfield',
    '#access' =&gt; TRUE,
    '#default_value' =&gt; 'test123',
    '#required' =&gt; TRUE,
  );

  $form['actions']['submit'] = array(
    '#type' =&gt; 'submit',
    '#value' =&gt; t('Send'),
  );

  $form['#validate'][] = 'comment_email_form_validate';
  $form['#submit'][] = 'comment_email_form_submit';
  return $form;
}


Thanks for any help.
You pass extra arguments when building the form using the drupal_get_form.

For example:

drupal_get_form('comment_email_form', 'default_value');

function comment_email_form($form, &amp;$form_state, $default_value)
{
    // $default_value is here the string 'default_value' value passed as extra argument
    // ... rest of your form
}