if else on variable link input - php

Question

I have a method of pulling Youtube video data from API links. I use Wordpress and ran into a snag.
In order to pull the thumbnail, views, uploader and video title I need the user to input the 11 character code at the end of watch?v=_______. This is documented with specific instructions for the user, but what if they ignore it and paste the whole url?
// the url 'code' the user should input.
_gXp4hdd2pk
// the wrong way, when the user pastes the whole url.
https://www.youtube.com/watch?v=_gXp4hdd2pk
If the user accidentally pastes the entire URL and not the 11 character code then is there a way I can use PHP to grab either the code or whats at the end of this url (11 characters after 'watch?v='?
Here is my PHP code to pull the data:
// $url is the code at the end of 'watch?v=' that the user inputs
$url = get_post_meta ($post->ID, 'youtube_url', $single = true);
// $code is a variable for placing the $url in a youtube link so I can output it to an API link
$code = 'http://www.youtube.com/watch?v=' . $url;
// $code is called at the end of this oembed code, allowing me to decode json data and pull elements from json to echo in my html
// echoed output returns json file. example: http://www.youtube.com/oembed?url=http://www.youtube.com/watch?v=_gXp4hdd2pk
$json = file_get_contents('http://www.youtube.com/oembed?url='.urlencode($code));
Im looking for something like...
"if user inputs code, use this block of code, else if user inputs whole url use a different block of code, else throw error."
Or... if they use the whole URL can PHP only use a specific section of that url...?
EDIT: Thank you for all the answers! I am new to PHP, so thank you all for your patience. It is difficult for graphic designers to learn PHP, even reading the PHP manual can give us headaches. All of your answers were great and the ones ive tested have worked. Thank you so much :)

Answer 1

Try this,
$code = 'https://www.youtube.com/watch?v=_gXp4hdd2pk';
if (filter_var($code, FILTER_VALIDATE_URL) == TRUE) {
// if `$code` is valid url
$code_arr = explode('?v=', $code);
$query_str = explode('&', $code_arr[1]);
$new_code = $query_str[0];
} else {
// if `$code` is not a valid url like '_gXp4hdd2pk'
$new_code = $code;
}
echo $new_code;

Answer 2

Here's a simple option for you to do, unless you want to use regex like Nisse Engström's Answer.
Using the function parse_url() you could do something like this:
$url = 'https://www.youtube.com/watch?v=_gXp4hdd2pk&list=RD_gXp4hdd2pk#t=184';
$split = parse_url('https://www.youtube.com/watch?v=_gXp4hdd2pk&list=RD_gXp4hdd2pk#t=184');
$params = explode('&', $split['query']);
$video_id = str_replace('v=', '', $params[0]);
now $video_id would return:
_gXp4hdd2pk
from the $url supplied in the above code.
I suggest you read the parse_url() documentation to ensure you understand and grasp it all :-)
Update
for your comment.
You'd use something like this to make sure the parsed value is a valid URL:
// this will check if valid url
if (filter_var($code, FILTER_VALIDATE_URL)) {
// its valid as it returned true
// so run the code
$url = 'https://www.youtube.com/watch?v=_gXp4hdd2pk&list=RD_gXp4hdd2pk#t=184';
$split = parse_url('https://www.youtube.com/watch?v=_gXp4hdd2pk&list=RD_gXp4hdd2pk#t=184');
$params = explode('&', $split['query']);
$video_id = str_replace('v=', '', $params[0]);
} else {
// they must have posted the video code as the if check returned false.
$video_id = $url;
}

Answer 3

Just try as follows ..
$url =" https://www.youtube.com/watch?v=_gXp4hdd2pk";
$url= explode('?v=', $url);
$endofurl = end($url);
echo $endofurl;
Replace $url variable with input .

Answer 4

I instruct my users to copy and paste the whole youtube url.
Then, I do this:
$video_url = 'https://www.youtube.com/watch?v=_gXp4hdd2pk'; // this is from user input
$parsed_url = parse_url($video_url);
parse_str($parsed_url['query'], $query);
$vidID = isset($query['v']) ? $query['v'] : NULL;
$url = "http://gdata.youtube.com/feeds/api/videos/". $vidID; // this is used for the Api

Answer 5

$m = array();
if (preg_match ('#^(https?://www.youtube.com/watch\\?v=)?(.+)$#', $url, $m)) {
$code = $m[2];
} else {
/* No match */
}
The code uses a Regular Expression to match the user input (the subject) against a pattern. The pattern is enclosed in a pair of delimiters (#) of your choice. The rest of the pattern works like this:
^ matches the beginning of the string.
(...) creates a subpattern.
? matches 0 or 1 of the preceeding character or subpattern.
https? matches "http" or "https".
\? matches "?".
(.+) matches 1 or more arbitrary charactes. The . matches any character (except newline). + matches 1 or more of the preceeding character or subpattern.
$ matches the end of the string.
In other words, optionally match an http or https base URL, followed by the video code.
The matches are then written to $m. $m[0] contains the entire string, $m[1] contains the first subpattern (base URL) and $m[2] contains the second subpattern (code).