How to get the input value with preprocess from a Fulltext Search Filter exposed form
Maybe not exactly what you're asking for, but the one way to approach this is to use hook_preprocess_views_view(&amp;$variables) and modify the contents of the header, or add a variable containing the string you want and then it in above/below the header in a views-view.tpl.php template override. If the search string isn't available through $variables, you can probably grab it from the url since it's likely included as a query string.
To get the query string from the url and add it to the template variables you'd do something like the following in your module or theme:
/**
 * Implements hook_preprocess_hook()
 */
function my_module_preprocess_views_view(&amp;$variables) {
  // Get the query string from the url.
  // it will be on something like ?the_search_string=big+banana.
  $search_string_raw = $_GET['the_search_string'];
  
  // Decode the url to remove special chars
  $search_string_decoded = urldecode($search_string_raw);

  // Add it to $variables so it's available in views-view.tpl.php
  $variables['search_string'] = $search_string_decoded;
}

This will make the search_string available in views-view.tpl.php. You can then print it in there with
&lt;?php if($search_string): ?&gt; 
  &lt;?php print $search_string ?&gt;
&lt;?php endif; ?&gt;

// or

&lt;?php

if($search_string) {
  print $search_string;
}

To clarify how hook_preprocess_hook works -- the first &quot;hook&quot; is your module name, and the second is the name of the template that you're targeting. Since we are targeting views-view.tpl.php, we use hook_preprocess_views_view.
In general, the easiest way to get started inspecting php variables is to dump them to the screen. For Drupal 7, I'd recommend installing https://www.drupal.org/project/kint on your site. This will let you print variables to the screen to help you dig into their values and see what's in there. You'd do like:
function my_module_preprocess_views_view(&amp;$variables) {
  kint($variables);
  // or
  kpr($variables['header'])
}

Then you can see what's actually inside of $variables and grab/modify the values in there.