This is a guide on how to remove special characters from a string using PHP. In this post, I will provide a number of different examples on how to strip out non-alphanumeric characters.
This can be a useful approach to take if you are dealing with user-inputted data for usernames and post codes, etc.
Remove ALL non-alphanumeric characters.
If you want to remove everything that isn’t a letter or a number, then you can use the following regular expression:
//String containing non-alphanumeric characters
$str = "this*is-a'test ()";
var_dump($str);
//Remove any character that isn't A-Z, a-z or 0-9.
$str = preg_replace("/[^A-Za-z0-9]/", '', $str);
var_dump($str);
The PHP string above contains an asterisk, a hyphen, an apostrophe, a blank space and two curly brackets. However, if we pass it into preg_replace and remove all non-alphanumeric characters, we are left with the following:
As you can see, all of the special characters have been removed. The white space included.
Remove everything except letters, numbers and white spaces.
If you want to keep white spaces, then you can use the following regex:
//String containing special characters.
$str = "this is- a' (test*&()";
//Remove any character that isn't A-Z, a-z, 0-9 or a whitespace.
$str = preg_replace("/[^A-Za-z0-9 ]/", '', $str);
var_dump($str);
The preg_replace example above transforms our string into the following:
This is because we instructed the preg_replace function to remove all non-alphanumeric character except spaces.
Regex to remove non-alphanumeric characters – except hyphens.
What if have a username field and you want to strip out everything except letters, numbers and hyphens?
//String containing special characters.
$username = "my-username()*&>>>>";
//Remove any character that isn't A-Z, a-z, 0-9 or a hyphen.
$username = preg_replace("/[^A-Za-z0-9-]/", '', $username);
var_dump($username);
The PHP snippet takes “my-username()*&>>>>” and converts it into the following string:
In the screenshot above, you can see that the hyphen character has been left untouched. This is unlike the asterisk and the ampersand characters, which have all been removed.
Allowing underscores.
In this example, we will remove all non-alphanumeric characters except the underscore character:
//String containing special characters.
$username = "&( my_username ><><";
//Remove any character that isn't A-Z, a-z, 0-9 or an underscore.
$username = preg_replace("/[^A-Za-z0-9_]/", '', $username);
var_dump($username);
The preg_match example above results in the following string:
Removing everything except letters, numbers and full stops / dots.
If you want allow full stops, you can use the following preg_match example:
//Example string.
$str = "website.com/#_";
//Remove any character that isn't A-Z, a-z, 0-9 or a dot.
$str = preg_replace("/[^A-Za-z0-9.]/", '', $str);
var_dump($str);
If you run the snippet above you will see that preg_match strips the forward slash, the hashtag and the underscore while ignoring the dot character.
To allow spaces AND dots, you can use the following regex:
//Example string.
$str = "*>hello. this' is*^ a test.(*&";
//Remove any character that isn't A-Z, a-z, 0-9, a space or a full stop.
$str = preg_replace("/[^A-Za-z0-9. ]/", '', $str);
var_dump($str);
This strips out all of the “bad” characters and leaves us with the following:
And that’s it. Hopefully, you found at least one of these examples useful!
Related: Extract numbers from a string using PHP.