Regex: Extract url parameters

Question

I am looking for a regex to extract URL params. My current solution is this:

(?i)key(?-i)=([^&]+)

but it fails on some of the tests below.

Lines where I want to match

cool=13&nice=zz&key=value&polo=0
Key=value&cool=13&nice=zz&polo=0
cool=13&nice=zz&polo=0&key=value

Lines I don't want to match it

cool=13&nice=zz&myKey=value&polo=0

Depending on which language you are using with this, it may already be available to you without regex. — user6702203
– user6702203, Commented Jun 19, 2018 at 19:16
If lookbehind is available then use: (?<=&|^)(?i)key(?-i)=[^&]* — anubhava
– anubhava, Commented Jun 19, 2018 at 19:23

anubhava · Accepted Answer · 2018-06-19 19:31:04Z

1

URL parsing routines are available in many languages and it is recommended to use them as first choice.

However if you want to use regex for some reason, here is a lookbehind regex that you may use:

(?<=&|^)(?i)key(?-i)=[^&]*

Here (?<=&|^) is a lookbehind assertion that makes sure that there is a & or line start before matching key.

answered Jun 19, 2018 at 19:31

anubhava

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2 Comments

(?-i) can be safely removed. [^&] will not be affected by the case insensitive modifier.

Yes, Agreed Wiktor.