Reg exp wanted for replacing all non-alphanumeric chars with underscores

Question

I want a reg exp for generating SEO-friendly URLs, so things like:

My product name

becomes

My_product_name

This is a long,long,long!!sentence

becomes

This_is_a_long_long_long_sentence

Basically so all non-alphanumeric chars are removed and replaced with underscores.

Any ideas?

Answer 1

preg_replace('/[^a-zA-Z0-9]+/', '_', $sentence)

Basically it looks for any sequence of non-alphanumeric characters and replaces it with a single '_'. This way, you also avoid having two consecutive _'s in your output.

If it's for URLs, you probably also want them to be lower-case only:

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

Answer 2

 $a = preg_replace("/[^A-Za-z0-9]+/", "_", $str);

or /\W+/ if you want to keep everything that is considered a "letter" in the current locale

after replacement it may be also neccessary to stip leading and trailing underscores

 $a = trim($a, '_');