There are 2 ways...
1- Terminal ... I'm not really sure about the right line...
2-Finder .... go to ... /user/library/preferences/com.apple.finder.plist
double-click and look for "Showallfiles", turn it ON and save, close, go to apple menu, force quit and relaunch Finder.
I'm sure via terminal is faster but the right line is unknow for me... I'll google that.