Question

I have the following regex from here: https://stackoverflow.com/a/10405818/924999

val regex = """/https?:\/\/(?:[0-9A-Z-]+\.)?(?:youtu\.be\/|youtube\.com(?:\/embed\/|\/v\/|\/watch\?v=|\/ytscreeningroom\?v=|\/feeds\/api\/videos\/|\/user\S*[^\w\-\s]|\S*[^\w\-\s]))([\w\-]{11})[?=&+%\w-]*/ig;""".r

I’m attempting to extract the video ID from youtube video urls with:

val url = "http://www.youtube.com/watch?v=XrivBjlv6Mw"

url match {

    case regex(result) => result

    case _ => null

}

However it seems to always return null, is there something I’m missing or need to do differently?

Thanks in advance for any help, much appreciated 🙂

Answer 1

The regex that you have is php-style regex, not java-style – for example, note /ig; flags at the end.

So you’ll just have to edit it a bit:

val youtubeRgx = """https?://(?:[0-9a-zA-Z-]+\.)?(?:youtu\.be/|youtube\.com\S*[^\w\-\s])([\w \-]{11})(?=[^\w\-]|$)(?![?=&+%\w]*(?:[\'"][^<>]*>|</a>))[?=&+%\w-]*""".r

I tested it on all possible youtube urls, and it works. Example:

scala> youtubeRgx.pattern.matcher("http://www.youtube.com/watch?v=XrivBjlv6Mw").matches
res23: Boolean = true

And extracting the value:

"http://www.youtube.com/watch?v=XrivBjlv6Mw" match {
  case youtubeRgx(a) => Some(a) 
  case _ => None 
}
res33: Option[String] = Some(XrivBjlv6Mw)

It’s a pity that java does not allow proper comments in regexps, so I did what I could:

val youtubeRgx = """https?://         # Required scheme. Either http or https.
                   |(?:[0-9a-zA-Z-]+\.)? # Optional subdomain.
                   |(?:               # Group host alternatives.
                   |  youtu\.be/      # Either youtu.be,
                   || youtube\.com    # or youtube.com followed by
                   |  \S*             # Allow anything up to VIDEO_ID,
                   |  [^\w\-\s]       # but char before ID is non-ID char.
                   |)                 # End host alternatives.
                   |([\w\-]{11})      # $1: VIDEO_ID is exactly 11 chars.
                   |(?=[^\w\-]|$)     # Assert next char is non-ID or EOS.
                   |(?!               # Assert URL is not pre-linked.
                   |  [?=&+%\w]*      # Allow URL (query) remainder.
                   |  (?:             # Group pre-linked alternatives.
                   |    [\'"][^<>]*>  # Either inside a start tag,
                   |  | </a>          # or inside <a> element text contents.
                   |  )               # End recognized pre-linked alts.
                   |)                 # End negative lookahead assertion.
                   |[?=&+%\w-]*       # Consume any URL (query) remainder.
                   |""".stripMargin.replaceAll("\\s*#.*\n", "").replace(" ","").r

(adapted from @ridgerunner’s answer here: find all youtube video ids in string)