How to check if a URL is valid

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).

---

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/

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.