Extract Numbers From String in PHP

Using filter_var() method

We can use the filter_var() method which filters a variable based on supplied filter flag or ID. To extract numbers from the string variable, we can pass the FILTER_SANITIZE_NUMBER_INT id.

Let’s see an example using this method.

0045456

This approach isn’t efficient for certain use case, and simply returns the numbers present within the string together. For a more efficient, we can rely on regular expression.
Use preg_match_all() method
Use preg_match_all() method with /[0-9]+/ to extract numbers from String in PHP.
$string = "Welcome to the 0045 and the 456 arena";
preg_match_all('/[0-9]+/', $string, $matches);

print_r($matches);

Array
(
    [0] => Array
        (
            [0] => 0045
            [1] => 456
        )

)

Here, output is array of matches, which can then be used to extract the numbers from the string. 
We used the preg_match_all() function to search for the regular expression and extracted the numbers from the string.
We used regular expression in the form of a pattern /[0-9]+/ that matched the numbers in the string.

preg_match_all performs global regular expression match. It takes three arguments:

$pattern : The pattern to be searched

$subject: Input String

$matches:Array of all matches in the String.
Use preg_replace() method
We can achieve the same output as the filter_var method using regular expression where we replace all the characters that are not numbers with empty whitespace. The regular expression match value would be /[^0-9]/.
Let’s illustrate this approach on the same string as in the previous section.
$string = 'Welcome to the 0045 and the 456 arena';
$int = preg_replace('/[^0-9]/', '', $string);
echo $int;

0045456

preg_replace() performs global regular expression match. It takes three arguments:

$pattern : The pattern to be searched

$replacement: the string to replace with searched string

$subject: Input String