"just" is the same meaning as "그냥" and "걍" is short form of "그냥"

it's short form of '그냥' if you speak '그냥' as fast as you can... it sounds like '걍' and it's not in dictionary, i'm not sure if the old use this one or not ex) A: why did you call me yesterday?(어제 왜 전화했어?) B: No reason. I just called you(이유 없어, 걍 걸었어!) you 'd better write all sentence from next time.. hard to understand what you want to know (wink)