Ruby regex to match hashtags in a string

gistfile1.txt

from http://www.rubular.com/r/PySQB8NvUY

(?:\s|^)(?:#(?!(?:\d+|\w+?_|_\w+?)(?:\s|$)))(\w+)(?=\s|$)

Test String:
#blah Pack my #box with #5 dozen #good2 #3good liquor.#jugs link.com/liquor#jugs #mkvef214asdwq sd #3e4 flsd #2good #_hello and #hello_ , how to just allow #hello2_world or #hello_23 #first#second #3


Match 1
1.	blah
Match 2
1.	box
Match 3
1.	good2
Match 4
1.	3good
Match 5
1.	mkvef214asdwq
Match 6
1.	3e4
Match 7
1.	2good
Match 8
1.	hello2_world
Match 9
1.	hello_23