What does this pattern match when filtering strings for URLs

Question

What exactly is this line for

preg_replace('#[^0-9a-z]+#i', '-', parent::filter($string))

in the following method in \vendor\magento\framework\Filter\TranslitUrl.php:

public function filter($string)
{
    $string = preg_replace('#[^0-9a-z]+#i', '-', parent::filter($string));
    $string = strtolower($string);
    $string = trim($string, '-');

    return $string;
}

The method is used to filter strings which will be used in URLs, and I know that line replaces some strings with - character. But I don't fully understand what exactly this pattern #[^0-9a-z]+#i matches.

I will appreciate any hints.

Answer 1

This pattern #[^0-9a-z]+#i matches all NOT numeric and NOT alphabetical symbols, in other words it will replace any symbol which is NOT in range 0-9 or a-z with the - symbol.

The ^ symbol inside group means it is negation (inversion).
The # symbols detects the start and end of the pattern.
The i flag says that regular expression should be case insensitive.

In the example string you can see a blue symbols, which will be replaced by that code with the - symbol:

So a result will be looking like this:

my-mom-says-i-don-t-know-where-it-is

The main purpose of this code is make string a valid URL-string, because you can insert inside the URL-key field whatever you want in any language.

Answer 2

The #[^0-9a-z]+#i
0-9 -> which indicates numeric values.
a-z -> which indicated small alphabetical values.
+# -> will allow # in url string.

Over all this pattern allow numeric|alphabets|# type patterns allows.