Golang doesn't support positive lookbehind assertion? about golang-regex-tutorial HOT 4 CLOSED

That is correct. This is not a bug. Refer to
https://github.com/google/re2/wiki/Syntax
to check the supported syntax.

from golang-regex-tutorial.

Thanks for your answer. I also notice Russ Cox's statement in Golang-nuts

The lack of generalized assertions, like the lack of backreferences, 
is not a statement on our part about regular expression style.  It is 
a consequence of not knowing how to implement them efficiently.  If 
you can implement them while preserving the guarantees made by the 
current package regexp, namely that it makes a single scan over the 
input and runs in O(n) time, then I would be happy to review and 
approve that CL.  However, I have pondered how to do this for five 
years, off and on, and gotten nowhere. 

from golang-regex-tutorial.

Oh, fellas, it makes life so harder.
For example, (\w+)(\.\w+)+(?!.*(\w+)(\.\w+)+) to get a filename from URL does not work.
More or less workaround is [^\/?#]*\.[^\/?#]*(\?.*)?(\#.*)?$.

from golang-regex-tutorial.

When retrieving a filename from a URL I would use 'split' at '/' and then take the last item. No need for regex.

from golang-regex-tutorial.