$ perl -d rec.pl

main::(rec.pl:10):      f(1);

  DB<1> c
main::f(rec.pl:6):          $_[0] unless $_[0] % 10000;

100 levels deep in subroutine calls!

##</code><code>##

$ perl -d rec.pl

main::(rec.pl:10):      f(1);

  DB<1> $DB::deep = 500

  DB<2> c
main::f(rec.pl:6):          $_[0] unless $_[0] % 10000;

500 levels deep in subroutine calls!