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.

• Alex Garrett: Thanks. I've updated my original question with some changes. Didn't notice the problem with different characters before, this has now been fixed.
• palacsint: @AlexGarrett: You're welcome. I've updated the answer a little bit.

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.

• Alex Garrett: Great, thanks for the advice. I actually adapted this code from the Laravel framework. It's for education purposes, so wanted to simplify it so it's easier for beginners to grasp. But I completely agree, good hardened code shouldn't be rewritten if not necessary.
• azngunit81: I recommend the codeigniter's version instead because i had to reverse engineer it for legacy non MVC code and it works better as as stand-alone function rather than a class (once you take out the clutter)