sub{$_[2]=$_[0]+$_[1],print shift for 1..20}->(1,1)  #51
@@=(1,1);push@@,$@[-2]+$@[-1]for 1..18;print for@@   #50
@@=(1,1);$@[2]=$@[0]+$@[1],print shift@@for 1..20    #49
@@=(1,0);print$@[@@]=$@[-1]+$@[-2]for 1..20          #43
print$@[@@]=$@[-1]+$@[-2]for(@@=(1,0))..21           #42

Missing first "1":
print$@[@@]=$@[-1]+$@[-2]for(@@=1)..19               #38

Loops forever:
@@=(1,0);print$@[@@]=$_+$@[-1]for@@                  #35

Missing first "1" and loops forever:
@@=1;print$@[@@]=$_+$@[-2]for@@                      #31