PHP validation/regex for URL

Use the filter_var() function to validate whether a string is URL or not:

var_dump(filter_var('example.com', FILTER_VALIDATE_URL));

It is bad practice to use regular expressions when not necessary.

EDIT: Be careful, this solution is not unicode-safe and not XSS-safe. If you need a complex validation, maybe it's better to look somewhere else.

I used this on a few projects, I don't believe I've run into issues, but I'm sure it's not exhaustive:

$text = preg_replace(  '#((https?|ftp)://(\S*?\.\S*?))([\s)\[\]{},;"\':<]|\.\s|$)#i',  "'<a href=\"$1\" target=\"_blank\">$3</a>$4'",  $text);

Most of the random junk at the end is to deal with situations like http://domain.com. in a sentence (to avoid matching the trailing period). I'm sure it could be cleaned up but since it worked. I've more or less just copied it over from project to project.

As per the PHP manual - parse_url should not be used to validate a URL.

Unfortunately, it seems that filter_var('example.com', FILTER_VALIDATE_URL) does not perform any better.

Both parse_url() and filter_var() will pass malformed URLs such as http://...

Therefore in this case - regex is the better method.