How To Use Underscores Instead Of Dashes In WordPress Permalinks ?

By default WordPress use dash (-) for separting words in permakinks (URL slugs) but you can easily change it to underscores (_). There are two methods. First you can do this by using a plugin or you have to paste some code you your site’s standard plugin or theme’s function.php file.

If you like using plugin then install and activate the new WordPress plugin called Underscores in Permalinks and you are done.

Alternatively you can use the plugin’s code in your theme’s function file, just copy-paste the following code, save the file and that’s all. Thanks to joeywohleb for providing this useful hack.

function uip_sanitize_title_with_underscores( $title, $raw_title = '', $context = 'display' ) {
    $title = strip_tags($title);
    // Preserve escaped octets.
    $title = preg_replace('|%([a-fA-F0-9][a-fA-F0-9])|', '---$1---', $title);
    // Remove percent signs that are not part of an octet.
    $title = str_replace('%', '', $title);
    // Restore octets.
    $title = preg_replace('|---([a-fA-F0-9][a-fA-F0-9])---|', '%$1', $title);

    if (seems_utf8($title)) {
        if (function_exists('mb_strtolower')) {
            $title = mb_strtolower($title, 'UTF-8');
        }
        $title = utf8_uri_encode($title, 200);
    }

    $title = strtolower($title);
    $title = preg_replace('/&.+?;/', '', $title); // kill entities
    $title = str_replace('.', '_', $title);

    if ( 'save' == $context ) {
        // Convert nbsp, ndash and mdash to hyphens
        $title = str_replace( array( '%c2%a0', '%e2%80%93', '%e2%80%94' ), '_', $title );

        // Strip these characters entirely
        $title = str_replace( array(
            // iexcl and iquest
            '%c2%a1', '%c2%bf',
            // angle quotes
            '%c2%ab', '%c2%bb', '%e2%80%b9', '%e2%80%ba',
            // curly quotes
            '%e2%80%98', '%e2%80%99', '%e2%80%9c', '%e2%80%9d',
            '%e2%80%9a', '%e2%80%9b', '%e2%80%9e', '%e2%80%9f',
            // copy, reg, deg, hellip and trade
            '%c2%a9', '%c2%ae', '%c2%b0', '%e2%80%a6', '%e2%84%a2',
            // acute accents
            '%c2%b4', '%cb%8a', '%cc%81', '%cd%81',
            // grave accent, macron, caron
            '%cc%80', '%cc%84', '%cc%8c',
        ), '', $title );

        // Convert times to x
        $title = str_replace( '%c3%97', 'x', $title );
    }

    $title = preg_replace('/[^%a-z0-9 _-]/', '', $title);
    $title = preg_replace('/\s+/', '_', $title);
    $title = preg_replace('|-+|', '_', $title);
    $title = trim($title, '_');

    return $title;
}

add_filter('sanitize_title', 'uip_sanitize_title_with_underscores', 10, 3);

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