Question

I am attempting to write a regular expression to process a string of key value(s) pairs formatted like so

KEY/VALUE KEY/VALUE VALUE KEY/VALUE

A key can have multiple values separated by a space.

I want to match a keys values together, so the result on the above string would be

VALUE
VALUE VALUE
VALUE

I currently have the following as my regex

[A-Z0-9]+/([A-Z0-9 ]+)(?:(?!^[A-Z0-9]+/))

but this returns

VALUE KEY 

as the first result.

Answer 1

In your negative lookahead assertion, change + to *; otherwise, you’re not preventing the match from ending right before a /, you’re only preventing it from ending right before a word that’s followed by a /. Also, remove the ^ from your negative lookahead assertion; it means “beginning of string”, so will never match in this context. That leaves:

[A-Z0-9]+/([A-Z0-9 ]+)(?![A-Z0-9]*/)

(I also dropped the (?:...) notation, since it had no effect in the context where it appeared.)

That said, a somewhat easier-to-read approach might be this:

[A-Z0-9]+/([A-Z0-9 ]+)( |$)

which requires the value to be followed by either a space (which gets swallowed) or end-of-string. Since keys are followed by /, it will ignore them.