Question

Many URL rewriting utilities allow Regex matching. I need some URLs to be matched against a couple of main querystring parmeter values no matter what order they appear in. For example let’s consider an URL having two key parameters ID= and Lang= in no specific order, and maybe some other non-key params are interspersed.

An Example URL to be matched with key params in any order:

• http://www.example.com/SurveyController.aspx?ID=500&Lang=4 or
• http://www.example.com/SurveyController.aspx?Lang=4&ID=500

Maybe with some interspersed non-key params:

• http://www.example.com/SurveyController.aspx?Lang=3&ID=1&misc=3&misc=4 or
• http://www.example.com/SurveyController.aspx?ID=1&misc=4&Lang=3 or
• http://www.example.com/SurveyController.aspx?misc=4&Lang=3&ID=1 or
• etc

Is there a good regex pattern to match against querystring param value in any order, or is it best to duplicate some rules, or in general should I look to other means?

Note: The main querystring values will also be captured using brackets i.e. ID=(3)&Lang=(500) and substituted into the destination URL, but that’s not the focus of the question.

Answer 1

I would suggest parsing the query string into a dictionary and working from there, but if you want regex, you can use alternation+repetition to match in any order (without inlining all possible sequences). Python example:

>>> import re
>>> p = re.compile(r'(?:[?&](?:abc=([^&]*)|xyz=([^&]*)|[^&]*))+$')
>>> p.findall('x?abc=1&jjj=2&xyz=3')
[('1', '3')]
>>> p.findall('x?abc=1&xyz=3&jjj=2')
[('1', '3')]
>>> p.findall('x?xyz=3&abc=1&jjj=2')
[('1', '3')]