Question

I want to convert user input string

“something … un// important ,,, like-this”

to

“something-un-important-like-this”

So basically remove all recurring special characters with “-“. I’ve googled and came to this

preg_replace('/[-]+/', '-', preg_replace('/[^a-zA-Z0-9_-]/s', '-', strtolower($string)));

I’m curious as to know if this can be done with a single preg_replace().

Just to clear things out:
replace all special characters and blank space with a hyphen(-). If more occurrence appear consecutively replace them with single hyphen

My solution works perfectly as I want to but I’m looking to do the same in a single call

Answer 1

There was a similar question yesterday, but I don’t have it at hand.

In your current first pattern:

[^a-zA-Z0-9_-]

you’re looking for a single character only. If you make that a greedy match for one or more, the regular expression engine will automatically replace multiple of these with a single one:

[^a-zA-Z0-9_-]+
              ^- + = one or more

You then still have the problem that existing - inside the string are not caught, so you need to take them out of the “not-in” character class:

[^a-zA-Z0-9_]+

This then should do it:

preg_replace('/[^a-zA-Z0-9_]+/s', '-', strtolower($string));

And as it’s only lowercase, you do not need to look for A-Z as well, just another reduction:

preg_replace('/[^a-z0-9_]+/s', '-', strtolower($string));

See as well Repetition and/or Quantifiers of which the + is one of (see Repetition^­Docs; Repetition with Star and Plus^{­regular-expressions.info}).

Also if you take a look at the modifiers^­Docs, you’ll see that the s (PCRE_DOTALL) modifier is not necessary:

$urlSlug = preg_replace('/[^a-z0-9_]+/', '-', strtolower($string));

Hope this helps and explains you a little about the regular expression you’re using and also where you can find further documentation which is always helpful.