Modifying Custom Search Options

Hello everyone,

I got a custom search that will search in the wp_postmeta table and sort the meta_value by alphabet.

However, I would like to add a second search function that is a dropdown box that will search in the meta_value for an exact match and return the results. Here is the custom search code that works for the search by alphabet. How can I modify this to be a drop down box that I can search for exact results?

<div class="search-nav">
                        Search By Category
                        <ul>
                            <li><a href="<?php echo home_url() .'/search-shippers'; ?>">Reset</a></li>
                            <?php
                                $str = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
                                for($i = 0; $i < strlen($str); $i++):
                                    $class = '';
                                    if ($str[$i] == $sel)
                                        $class = ' class="actv"';
                            ?>
                            <li<?php echo $class; ?>><a href="<?php echo home_url() .'/search-shippers?sel=' . $str[$i] . '"'; ?>><?php echo $str[$i]; ?></a></li>
                            <?php
                                endfor;
                            ?>
                        </ul>
                        <div class="clearfloat"></div>
                    </div>

Any help would be greatly appreciated 🙂