How to check if a URL is valid

Question

How can I check if a string is a valid URL?

For example:

http://hello.it => yes http:||bra.ziz, => no 

If this is a valid URL how can I check if this is relative to a image file?

Answer 1

Notice:

As pointed by @CGuess, there's a bug with this issue and it's been documented for over 9 years now that validation is not the purpose of this regular expression (see https://bugs.ruby-lang.org/issues/6520).

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Use the URI module distributed with Ruby:

require 'uri'  if url =~ URI::regexp     # Correct URL end 

Like Alexander Günther said in the comments, it checks if a string contains a URL.

To check if the string is a URL, use:

url =~ /\A#{URI::regexp}\z/ 

If you only want to check for web URLs (http or https), use this:

url =~ /\A#{URI::regexp(['http', 'https'])}\z/ 

Answer 2

Similar to the answers above, I find using this regex to be slightly more accurate:

URI::DEFAULT_PARSER.regexp[:ABS_URI] 

That will invalidate URLs with spaces, as opposed to URI.regexp which allows spaces for some reason.

I have recently found a shortcut that is provided for the different URI rgexps. You can access any of URI::DEFAULT_PARSER.regexp.keys directly from URI::#{key}.

For example, the :ABS_URI regexp can be accessed from URI::ABS_URI.