Slug URL Generator

Question

Just a slug generator. I'm wondering if this can be simplified any further.

Many thanks.

<?php
function slug($string) {

    // Replace all non letters, numbers, spaces or hypens
    $string = preg_replace('/[^\-\sa-zA-Z0-9]+/', '', mb_strtolower($string));

    // Replace spaces and duplicate hyphens with a single hypen
    $string = preg_replace('/[\-\s]+/', '-', $string);

    // Trim off left and right hypens
    $string = trim($string, '-');

    return $string;
}

echo slug('-- This is an example     of an ------ article   - @@@ ..,.:~&**%$£%$^*'); // outputs "this-is-an-example-of-an-article"

Updated version based on feedback:

<?php
function createSlug($slug) {

    $lettersNumbersSpacesHyphens = '/[^\-\s\pN\pL]+/u';
    $spacesDuplicateHypens = '/[\-\s]+/';

    $slug = preg_replace($lettersNumbersSpacesHyphens, '', $slug);
    $slug = preg_replace($spacesDuplicateHypens, '-', $slug);

    $slug = trim($slug, '-');

    return mb_strtolower($slug, 'UTF-8');
}

echo createSlug('-- This is an example ű of an ------ article   - @@@ ..,.%&*£%$&*(*');
?>

Answer 1

1. You could create a few explanatory local variables:

   $lettersNumbersSpacesHypens = '/[^\-\sa-zA-Z0-9]+/';
   $spacesAndDuplicateHyphens = '/[\-\s]+/';
   

   Usage:

   $lettersNumbersSpacesHypens = '/[^\-\sa-zA-Z0-9]+/';
   $slug = preg_replace($lettersNumbersSpacesHypens, '', mb_strtolower($slug));
   
   $spacesAndDuplicateHyphens = '/[\-\s]+/';
   $slug = preg_replace($spacesAndDuplicateHyphens, '-', $slug);
   

   These would eliminate the comments. (I haven't checked the regexps, other names might be more appropriate.)

   Reference: Chapter 6. Composing Methods, Introduce Explaining Variable in Refactoring: Improving the Design of Existing Code by Martin Fowler:

   Put the result of the expression, or parts of the expression, in a temporary variable with a name that explains the purpose.

   And Clean Code by Robert C. Martin, G19: Use Explanatory Variables.

2. slug could be renamed to cleanSlug (contains a verb) to describe what the function does.

3. I'd rename the $string variable to $slug It would be more descriptive, it would express the intent of the variable.

4. I'd use a whitelist instead of the blacklist. Defining the allowed characters (A-Z, 0-9 etc) would create proper URLs from URLs which contain special characters like é or ű.

Answer 2

Just a small extension to what has been written. If your slug generator is not for an assignment but for actual deployment a lot of frameworks use slug helpers already. I use Laravel, however Laravel has an entire class so that might be messy.

Before Laravel, Codeigniter was the rapid deploy system and their slug system is pretty robust.

Take a look at the slug file. Now mind you they have formatted it into a class with a lot of comments - but if you omit everything you can compare their's and yours and see where the middle ground can be.

Codeigniter Slug Class

Note - I'm adding this extra bit because as always you shouldn't re-engineer code if its been done and done well.