php preg_match_all简单正则表达式返回空值

Question

I need to extract a predefined set of hashtags from a blob of text, then extract what number follows right after it if any. Eg. I'd need to extract 30 from "Test string with #other30 hashtag". I assumed preg_match_all would be the right choice.

Some test code:

$hashtag = '#other';
$string  = 'Test string with #other30 hashtag';
$matches = [];
preg_match_all('/' . $hashtag . '\d*/', $string, $matches);
print_r($matches);

Output:

Array
(
    [0] => Array
        (
            [0] => #other30
        )
)

Perfect... Works as expected. Now to extract the number:

$string = $matches[0][0]; // #other30
$matches = [];
preg_match_all('/\d*/', $string, $matches);
print_r($matches);

Output:

Array
(
    [0] => Array
        (
            [0] =>
            [1] =>
            [2] =>
            [3] =>
            [4] =>
            [5] =>
            [6] => 30
            [7] =>
        )
)

What? Looks like it's trying to match every character?

I'm aware of some preg_match_all related answers (one, two), but they all use a parenthesized subpattern. According to documentation - it is optional.

What am I missing? How do I simply get all matches into an array that match such a basic regex like /\d*/ There doesn't seem to be a more appropriate function in php for that.

I never thought I'd be scratching my head with such a basic thing in PHP. Much appreciated.

Answer 1

You need to replace:

preg_match_all('/\d*/', $string, $matches);

with:

preg_match_all('/\d+/', $string, $matches);

Replace * with +

Because

* Match zero or more times.

+ Match one or more times.