<?php $unique_id = esc_attr(uniqid('search-form-')); ?>

<form role="search" method="get" class="search-form" action="<?php echo esc_url(home_url('/')); ?>">
    <label class="sr-only" for="<?php echo $unique_id; ?>"><?php echo _x('Search for:', 'label', 'keitaro'); ?></label>

    <div class="input-group">
        <input type="search" id="<?php echo $unique_id; ?>" class="form-control search-field" placeholder="<?php echo esc_attr_x('Search &hellip;', 'placeholder', 'keitaro'); ?>" value="<?php echo get_search_query(); ?>" name="s" />
        <span class="input-group-btn">
            <button type="submit" class="btn btn-default"><span class="glyphicon glyphicon-search"></span></button>
        </span>
    </div>

</form>
<?php $unique_id = esc_attr(uniqid('search-form-')); ?>

<form role="search" method="get" class="search-form" action="<?php echo esc_url(home_url('/')); ?>">
    <label class="sr-only" for="<?php echo $unique_id; ?>"><?php echo _x('Search for:', 'label', 'keitaro'); ?></label>

    <div class="input-group">
        <input type="search" id="<?php echo $unique_id; ?>" class="form-control search-field" placeholder="<?php echo esc_attr_x('Search &hellip;', 'placeholder', 'keitaro'); ?>" required="required" value="<?php echo get_search_query(); ?>" name="s" />
        <span class="input-group-btn">
            <button type="submit" class="btn btn-default"><span class="glyphicon glyphicon-search"></span></button>
        </span>
    </div>

</form>
Make search field input required
Make search field input required
