Add a Search shortcode to WordPress

wordpress_search_form_shortcode.php

<?php

/* Wordpress Search Form - Shortcode
-------------------------------------------------- */

/*
 * USAGE:
 * Post Content: [shortcode_search]
 * Template: echo do_shortcode("[shortcode]");
 */
 
function shortcode_search_form( $form ) {
  $form = '
    <form class="form-inline" role="search" method="get" action="' . home_url( '/' ) . '">
      <div class="form-group">
        <label class="sr-only" for="s">Search</label>
        <input type="text" class="form-control" id="s" name="s" placeholder="Search..." value="' . get_search_query() . '">
      </div>
      <button type="submit" class="btn btn-primary">Search</button>
    </form>
  ';
  return $form;
}
add_shortcode('shortcode_search', 'shortcode_search_form');