使用正则表达式验证 Youtube URL

However, I don't think I've got my logic right, because for some reason it returns true for: www.youtube.co/watch?v=vpfzjcCzdtCk (Notice I've written it incorrectly with .co and not .com)

推荐答案

在你的这个正则表达式中有很多冗余(还有 倾斜牙签综合症).不过，这应该会产生结果:

There are a lot of redundancies in this regular expression of yours (and also, the leaning toothpick syndrome). This, though, should produce results:

$rx = '~
  ^(?:https?://)?                           # Optional protocol
   (?:www[.])?                              # Optional sub-domain
   (?:youtube[.]com/watch[?]v=|youtu[.]be/) # Mandatory domain name (w/ query string in .com)
   ([^&]{11})                               # Video id of 11 characters as capture group 1
    ~x';

$has_match = preg_match($rx, $url, $matches);

// if matching succeeded, $matches[1] would contain the video ID

一些注意事项:

• 使用波浪号 ~ 作为分隔符，避免 LTS
• 使用 [.] 而不是 . 来提高视觉易读性并避免 LTS.(特殊"字符 - 例如点 . - 在字符类中无效(方括号内))
• 为了使正则表达式更可读"，您可以使用 x 修饰符(这有进一步的含义；请参阅 关于模式修饰符的文档)，它还允许在正则表达式中添加注释
• 可以使用非捕获组来抑制捕获:(?: ).这使表达式更有效.

• use the tilde character ~ as delimiter, to avoid LTS
• use [.] instead of . to improve visual legibility and avoid LTS. ("Special" characters - such as the dot . - have no effect in character classes (within square brackets))
• to make regular expressions more "readable" you can use the x modifier (which has further implications; see the docs on Pattern modifiers), which also allows for comments in regular expressions
• capturing can be suppressed using non-capturing groups: (?: <pattern> ). This makes the expression more efficient.

或者，要从(或多或少完整的)URL 中提取值，您可能需要使用 parse_url():

Optionally, to extract values from a (more or less complete) URL, you might want to make use of parse_url():

$url = 'http://youtube.com/watch?v=VIDEOID';
$parts = parse_url($url);
print_r($parts);

输出:

Array
(
    [scheme] => http
    [host] => youtube.com
    [path] => /watch
    [query] => v=VIDEOID
)

验证域名和提取视频 ID 留给读者作为练习.

Validating the domain name and extracting the video ID is left as an exercise to the reader.

我屈服于下面的评论战；感谢 Toni Oriol，正则表达式现在也适用于短 (youtu.be) 网址.

I gave in to the comment war below; thanks to Toni Oriol, the regular expression now works on short (youtu.be) URLs as well.

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