What regex would find out if file url has certain extension

My valid urls could look more or less like this

http://someurl.com/some/path/file.pdf
or 
http://someurl.com/some/path/file.开发者_运维知识库pdf?param=value
or 
http://someurl.com/some/path/file.pdf?param=value&second=val

where the file extension could be .pdf, or some other extension like .jpg or .psd, or nothing at all.

I have the url stored without the someurl.com portion, so it's the some/path/file.pdf part of the url

How can I use regex to know the file extension if it is present? Is regex the right tool for this?

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I would use parse_url() and pathinfo(). These are the most correct functions for the job.

$url = 'http://someurl.com/some/path/file.pdf?param=value';

$path = parse_url($url, PHP_URL_PATH);

$ext = pathinfo($path, PATHINFO_EXTENSION);

var_dump($ext); // string(3) "pdf"

See is on CodePad.org.

You could use regex, but it will be more difficult to follow.

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You would probably need to do a HTTP HEAD request. Regex would work for sure, but you're not guaranteed to catch all cases.

For example:

http://someurl.com/some/path/file might a be a text file without extension (like on most *nix systems) and the regex would fail to provide the file extension.

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A much better option is PHP's parse_url function:

$path = parse_url($url, PHP_URL_PATH);
$extension = ($pos = strrpos($path, '.')) ? substr($path, $pos) : "";

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Don't need regex, we can just use parse_url.

$url = parse_url('http://example.com/path/to/file.php?param=value');

$extension = substr($url['path'], strrpos($url['path'], '.') + 1);
echo $extension; // outputs "php"

http://php.net/parse-url

http://php.net/substr

http://php.net/strrpos