Converts a string into a slug

slugify.php

<?php

/**
 * Returns a slugified version of a string
 *
 * E.g: Hello World becomes hello-world
 *
 * @param string $input
 *
 * @return string
 */
function slugify($input)
{
    $input = strip_tags($input);
    // Preserve escaped octets.
    $input = preg_replace('|%([a-fA-F0-9][a-fA-F0-9])|', '---$1---', $input);
    // Remove percent signs that are not part of an octet.
    $input = str_replace('%', '', $input);
    // Restore octets.
    $input = preg_replace('|---([a-fA-F0-9][a-fA-F0-9])---|', '%$1', $input);

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

    // Convert nbsp, ndash and mdash to hyphens
    $input = str_replace(['%c2%a0', '%e2%80%93', '%e2%80%94'], '-', $input);

    // Strip these characters entirely
    $input = str_replace([
        // 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',
    ], '', $input);

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

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

    return $input;
}