How replace an optionally occuring prefix with regex

Question

I have a query string that can look like this:

    ?blah=1&phoneNum=123-456-7890

OR

    ?phoneNum=123-456-7890

I'm using this regex: phoneNum=[^&]+&? to remove the substring phoneNum=__ from the query string, but it leaves a trailing & in the first case, which is no me gusta.

How do I adapt my regex pattern to optionally remove the preceeding &? so it removes both:

    phoneNum=123-456-7890

AND

    &phoneNum=123-456-7890

from the query string?

Could you tell us exactly what result you would like with the given inputs? — Justmaker
– Justmaker, Commented Feb 6, 2012 at 18:37
try using &?phoneNum=[^&]+&?... Although i am not sure WHY you are splitting your own query string instead of using a query string parser. Are you writing your own parser? What programming language are you using? — Ahmed Masud
– Ahmed Masud, Commented Feb 6, 2012 at 18:37

Amarghosh · Accepted Answer · 2012-02-06 18:38:00Z

1

Just like the way you made the last & optional using ?, you can make the first one also optional:

&?phoneNum=[^&]+&?

answered Feb 6, 2012 at 18:38

Amarghosh

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Comments

juanrpozo · Accepted Answer · 2012-02-06 18:42:09Z

1

To strictly answer your question, you would prepend a &? to your regex, but I think it's a fragile approach, because the phoneNum param can potentially be anywhere in the query string: first, last or inbetween. If you ever start passing more parameters and you remove both & signs, you can end up with a messed up request.

I would parse the query, discard the phoneNumber parameter and construct the query again.

answered Feb 6, 2012 at 18:42

juanrpozo

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