Regex: Finding a value for a "key" inside brackets over multiple lines

I'm currently having some trouble wrapping my head around regular expressions, which is where I hope some of you regex guru's out there might be able to assist with.

I'll briefly explain my problem with an example of what I am trying to achieve. I have an input string, with a key and开发者_开发百科 value I am looking for, which look somewhat like this:

• G01::Notice ((The customer already exists))
• G01::MyNotice ((The customer already exists, nevermind...))
• G02::OrderConfirm ((The order has been comfirmed! Please inform the customer that his orders will arrive soon.))

In the above examples, I would like to get everything for G01:: which is enclosed within the parentheses. So my pattern is

Looking at the three input strings, I should add a few notices:

I am not sure if your question is complete ...

Is it this what you want?

G01::[^(]*\(\(([^)]*)

See it here on Regexr. The text within the brackets is in the capture group 1.

Try this regex: G01::\w+ \(\((.*?)\)\)

Not a complete question, but how about this one?

.*\((.*?)\)

Result 1
The customer already exists

Result 2
The customer already exists, nevermind...

Result 3
The order has been comfirmed! Please inform the customer that his orders will arrive soon.

On rubular

G01.*\(\((.*)\)\) seems to work (unless I misunderstood your question).