Matching URLs with Optional HTTP and WWW Prefixes

Regular expressions are powerful tools for complex pattern matching tasks. When it comes to matching URLs, there are often variations in the format, such as whether it includes "http://www." prefix or not.

Solution Using Regular Expression

To match URLs with or without the "http://www." prefix, the following regular expression can be used:

((https?|ftp)://)?
([a-z0-9+!*(),;?&=$_.-]+(:[a-z0-9+!*(),;?&=$_.-]+)?@)?
([a-z0-9\-\.]*)\.(([a-z]{2,4})|([0-9]{1,3}\.([0-9]{1,3})\.([0-9]{1,3})))
(:[0-9]{2,5})?
(/([a-z0-9+$_%-]\.?)+)*/?
(\?[a-z+&\$_.-][a-z0-9;:@&%=+/$_.-]*)?
(#a-z_.-][a-z0-9+$%_.-]*)?

Breakdown of the Expression:

• (https?|ftp):// - Optional protocol identifier (http or ftp)
• ([a-z0-9+!*(),;?&=$_.-]+(:[a-z0-9+!*(),;?&=$_.-]+)?@)? - Optional user and password
• ([a-z0-9-.]*).(([a-z]{2,4})|([0-9]{1,3}.([0-9]{1,3}).([0-9]{1,3}))) - Hostname or IP address
• (:[0-9]{2,5})? - Optional port number
• (/([a-z0-9+$_%-].?)+)*/? - Optional path
• (?a-z+&$_.-*)? - Optional query string
• (#a-z_.-][a-z0-9+$%_.-]*)? - Optional anchor

Example Usage

To check if a given string matches the regular expression, use the following syntax:

if(preg_match(~^$regex$~i, 'www.example.com/etcetc', $m))

This will return TRUE if the string matches the URL pattern with or without the "http://www." prefix.