检查字符串的不同部分时，preg_match失败了

Question

This preg_match will never work even though I think its the right thing.

I'm trying to check a string so that it's structured as follows

$value = US 01 02 1406034963 .JPG //I've put spaces in. The real one is below.

So:

The first part (US) is alphabets, only two characters from a-z

The second part (01) is a value 00 or 01

The third part (02) is digits 0-9 from 2 - 10 (can be 2 to 10 digits long)

The fourth part (1406034963) is a 10 digit figure, and only 10 digits

The fifth part is .jpg or .jpeg or .png. or .gif

But, my function always returns false. Can you please help?

//
function preset($value) {
    if(preg_match('/^[a-z]{2}[00|01][0-9]{2,10}[0-9]{10}[.jpg|.jpeg|.png.|.gif]$/',$value)) {
        return true;
    } else {
        return false;
    }
}

$value = 'US01021406034963.JPG';

if(preset($value)) {
    echo 'Yeah!';
} else {
    echo 'Boo!';
}

Answer 1

[] denotes a character class. Simply put, a character class is a way of denoting a set of characters in such a way that one character of the set is matched.

You're trying to use alternation inside character classes. It will not work as you expect it to. For example, the regex [00|01] would match 0, the literal character |, or 1, and not 00 or 01.

To match either of the set, you can simply use grouping. In this case, you're not going to use the matched text anywhere, so you can use non-capturing groups. (?:00|01) is a non-capturing group that will match either 00 or 01. You can also shorten it and write just 0[01], but that totally depends on your taste.

And currently, your expression only matches lower-case strings. If you want it to work with upper-case, or even mixed-case strings, you can simply use the i modifier. It will make the pattern match the string case-insensitively.

You can simplify your function to just:

function preset($value) {
    return (bool) preg_match('/^[a-z]{2}(?:00|01)[0-9]{2,10}[0-9]{10}\.(?:jpe?g|png|gif)$/i',$value);
}

Demo