Regular Expression break down URL into parts

I've just recently started learning Regex so i'm not sure yet about a couple of aspects of the hole thing.

Right now my web page reads in the URL breaks开发者_运维技巧 it up into parts and only uses certain parts for processing: E.g. 1) http://mycontoso.com/products/luggage/selloBag E.g. 2) http://mycontoso.com/products/luggage/selloBag.sf404.aspx

For some reason Sitefinity is giving us both possibilities, which is fine, but what I need from this is only the actual product details as in "luggage/selloBag"

My current Regex expression is: "(.*)(map-search)(\/)(.*)(\.sf404\.aspx)", I combine this with a replace statement and extract the contents of group 4 (or $4), which is fine, but it doesn't work for example 2.

So the question is: Is it possible to match 2 possibilities with regular expressions where a part of a string might or might not be there and then still reference a group whose value you actually want to use?

RFC-3986 is the authority regarding URIs. Appendix B provides this regex to break one down into its components:

re_3986 = r"^(([^:/?#]+):)?(//([^/?#]*))?([^?#]*)(\?([^#]*))?(#(.*))?"
# Where:
# scheme    = $2
# authority = $4
# path      = $5
# query     = $7
# fragment  = $9

Here is an enhanced (and commented) regex (in Python syntax) which utilizes named capture groups:

    re_3986_enhanced = re.compile(r"""
        # Parse and capture RFC-3986 Generic URI components.
        ^                                    # anchor to beginning of string
        (?:  (?P<scheme>    [^:/?#\s]+): )?  # capture optional scheme
        (?://(?P<authority>  [^/?#\s]*)  )?  # capture optional authority
             (?P<path>        [^?#\s]*)      # capture required path
        (?:\?(?P<query>        [^#\s]*)  )?  # capture optional query
        (?:\#(?P<fragment>      [^\s]*)  )?  # capture optional fragment
        $                                    # anchor to end of string
        """, re.MULTILINE | re.VERBOSE)

For more information regarding the picking apart and validation of a URI according to RFC-3986, you may want to take a look at an article I've been working on: Regular Expression URI Validation

Depends on your regex implementation, but most support a syntax like

(\.sf404\.aspx|)

Assuming that's your group 4 (i.e. zero-indexed groups). The | lists two alternatives, one of which is the empty string.

You don't say if you're doing this in javascript, but if you are, the parseUri lib written by Steven Levithan does a pretty damn good job at parsing urls. You can get it from various places, including here (click on the "Source Code" tab) and here.