[php] How to remove non-alphanumeric characters?

I need to remove all characters from a string which aren't in a-z A-Z 0-9 set or are not spaces.

Does anyone have a function to do this?

If you need to support other languages, instead of the typical A-Z, you can use the following:

preg_replace('/[^\p{L}\p{N} ]+/', '', $string);

• [^\p{L}\p{N} ] defines a negated (It will match a character that is not defined) character class of:
  • \p{L}: a letter from any language.
  • \p{N}: a numeric character in any script.
  • : a space character.
• + greedily matches the character class between 1 and unlimited times.

This will preserve letters and numbers from other languages and scripts as well as A-Z:

preg_replace('/[^\p{L}\p{N} ]+/', '', 'hello-world'); // helloworld
preg_replace('/[^\p{L}\p{N} ]+/', '', 'abc@~#123-+=öäå'); // abc123öäå
preg_replace('/[^\p{L}\p{N} ]+/', '', '????!@£$%^&*()'); // ????

^{Note: This is a very old, but still relevant question. I am answering purely to provide supplementary information that may be useful to future visitors.}

[\W_]+

$string = preg_replace("/[\W_]+/u", '', $string);

It select all not A-Z, a-z, 0-9 and delete it.

See example here: https://regexr.com/3h1rj

I was looking for the answer too and my intention was to clean every non-alpha and there shouldn't have more than one space.
So, I modified Alex's answer to this, and this is working for me preg_replace('/[^a-z|\s+]+/i', ' ', $name)
The regex above turned sy8ed sirajul7_islam to sy ed sirajul islam
Explanation: regex will check NOT ANY from a to z in case insensitive way or more than one white spaces, and it will be converted to a single space.

here's a really simple regex for that:

\W|_

and used as you need it (with a forward / slash delimiter).

preg_replace("/\W|_/", '', $string);

Test it here with this great tool that explains what the regex is doing:

http://www.regexr.com/

preg_replace("/\W+/", '', $string)

You can test it here : http://regexr.com/

You can split the string into characters and filter it.

<?php 

function filter_alphanum($string) {
    $characters = str_split($string);
    $alphaNumeric = array_filter($characters,"ctype_alnum");
    return join($alphaNumeric);
}

$res = filter_alphanum("a!bc!#123");
print_r($res); // abc123

?>

For unicode characters, it is :

preg_replace("/[^[:alnum:][:space:]]/u", '', $string);

Regular expression is your answer.

$str = preg_replace('/[^a-z\d ]/i', '', $str);

• The i stands for case insensitive.
• ^ means, does not start with.
• \d matches any digit.
• a-z matches all characters between a and z. Because of the i parameter you don't have to specify a-z and A-Z.
• After \d there is a space, so spaces are allowed in this regex.