$_ = '12d.9j7h.7tttt.125.ty.2.4.8.9f.y6.34gk.ll';

print "split: ", map "[$_]", grep $_, split /((?:\w+.){3}\w+)\.?/;
print "regex: ", map "[$_]", m< ( (?: \w+. ){3} \w+ ) \.? >xg;

__output___

split: [12d.9j7h.7tttt.125][ty.2.4.8][9f.y6.34gk.ll]
regex: [12d.9j7h.7tttt.125][ty.2.4.8][9f.y6.34gk.ll]