How To Remove Non-Alphanumeric Characters From A String in PHP?

Using Regular Expressions (preg_replace)

The preg_replace function in PHP uses regular expressions to remove non-alphanumeric characters from a string. The regex pattern "[^A-Za-z0-9 ]" matches any character that is not a letter, number, or space.

Here's how to use preg_replace:

$string = "Hello, World! 123 @#$";
$result = preg_replace("/[^A-Za-z0-9 ]/", '', $string);
echo $result; // Output: Hello World 123

In this code, the first argument is the regex pattern, the second is the replacement (an empty string), and the third is the input string.

$result = preg_replace("/[^A-Za-z0-9 ]/i", '', $string);

Using str_replace Function

If you prefer not to use regex, the str_replace function offers another method. This approach involves creating an array of characters to remove and replacing them with an empty string.

Here's how to use str_replace:

$string = "Hello, World! 123 @#$";
$chars_to_remove = array("!", "@", "#", "$", ",");
$result = str_replace($chars_to_remove, '', $string);
echo $result; // Output: Hello World 123 

This method requires you to specify each character you want to remove. While it's less flexible than regex, it can be easier to understand and change for specific needs.

Handling Spaces

When removing non-alphanumeric characters, you can include or exclude spaces. To include spaces in the result, add a space to the regex pattern:

$result = preg_replace("/[^A-Za-z0-9 ]/", '', $string);

To exclude spaces and remove them with other non-alphanumeric characters, remove the space from the pattern:

$result = preg_replace("/[^A-Za-z0-9]/", '', $string);

$result = preg_replace("/[^A-Za-z0-9\s+]/", '', $string);

Case Sensitivity

The default regex pattern used in preg_replace is case-sensitive. It treats uppercase and lowercase letters differently. To make the function case-insensitive, add the 'i' flag at the end of the pattern:

$result = preg_replace("/[^A-Za-z0-9]/i", '', $string);

This change allows the pattern to match both uppercase and lowercase letters without distinction. If you need to keep only lowercase or uppercase letters, you can adjust the pattern:

For lowercase only:

$result = preg_replace("/[^a-z0-9]/", '', strtolower($string));

For uppercase only:

$result = preg_replace("/[^A-Z0-9]/", '', strtoupper($string));

These changes give you more control over the characters you want to keep in your string.