htaccess how to rewrite this url

How to rewrite this URL:

https://example.com/illustrations.php?category=cats&cat_id=1

to:

https://example.com/category/cats

also, how do I still preserve cat_id param?

I tried this but it does not work:

RewriteEngine on
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^/?category/(.*?)/?$ /illustrations.php?category=$1 [L]

Answer

When I add this code and go to illustrations.php?category=cats it does not change the URL in the browserbar.

Yes, that is “correct”.

The code you posted internally rewrites the URL /category/cats (which is the URL you should be linking to in your HTML source) back to the actual filesystem/URL path: /illustrations.php?category=cats. This is required in order to make the “pretty” URL /category/cats “work”.

You can’t change the URL structure using .htaccess only – if that is what you are implying. You do need to actually change the physical URLs in your HTML source.

You could implement an external redirect (not a rewrite) from /illustrations.php?category=cats to the canonical URL /category/cats using .htaccess, but note that this is only to benefit SEO (and third parties that might have already linked to the old URLs). This is a necessary additional step if you are changing an existing URL structure and SEO is a concern, but it is not part of the “working” of your site.

how do I still preserve cat_id param

You would need to include the value of the cat_id parameter in the URL. eg. /category/cats/1 (as @arkascha suggested in comments) or /category/1/cats – depending on which value is more important. I would put the more important value first, since URLs can be accidentally cropped when shared.

RewriteEngine on
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^/?category/(.*?)/?$ /illustrations.php?category=$1 [L]

This rule could be simplified. Filesystem checks are relatively expensive. It looks like you could remove both of these by making your regex more specific. eg. Could /category/1/cats ever map to a file? Do you need directories to be accessible? I would expect the answer to both those questions is “no”.

I would also decide on whether to allow trailing slashes or not, rather than allowing both (as in your current rule). Strictly speaking this creates duplicate content (two URLs; same content), so requires additional steps to resolve. Your example URL(s) do not contain a trailing slash.

So, you could simplify your rules to the following in order to rewrite /category/1/cats (no trailing slash) to /illustrations.php?category=cats&cat_id=1

RewriteEngine On
RewriteRule ^category/(d+)/([w-]+)$ /illustrations.php?category=$2&cat_id=$1 [L]

This assumes cat_id can be 1 or more digits (0-9). And category is limited to the following characters: a-z, A-Z, 0-9, _ (underscore), - (hyphen).

With regex it is preferable to be as restrictive as possible. By omitting the dot (.) from the last path segment in the above rule it cannot match a physical file (assuming all your files have file extensions).