-> perl -de 1 

Loading DB routines from perl5db.pl version 1.19
Editor support available.

Enter h or `h h' for help, or `man perldebug' for more help.

main::(-e:1):   1
  DB<1> $a{'a'}{0}=0

  DB<2> print scalar %{$a{'a'}}
1/8
  DB<3> $a{'a'}{1}=0           

  DB<4> print scalar %{$a{'a'}}
2/8
  DB<5> $a{'a'}{2}=0           

  DB<6> print scalar %{$a{'a'}}
3/8
  DB<7> $a{'a'}{3}=0           

  DB<8> print scalar %{$a{'a'}}
3/8
  DB<9> $a{'a'}{4}=0           

  DB<10> print scalar %{$a{'a'}}
3/8
  DB<11> $a{'a'}{5}=0           

  DB<12> print scalar %{$a{'a'}}
4/8