$ cat perldebug.loop.pl
#!/usr/bin/perl --
my %f = ( 1 .. 10 );
while(my($k,$v)=each%f){
    print qq[$k $v\n];
}
print "done\n";

$ perl -d perldebug.loop.pl

Loading DB routines from perl5db.pl version 1.33
Editor support available.

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

main::(perldebug.loop.pl:2):    my %f = ( 1 .. 10 );
  DB<1> n
main::(perldebug.loop.pl:3):    while(my($k,$v)=each%f){
  DB<1> n
main::(perldebug.loop.pl:4):        print qq[$k $v\n];
  DB<1> n
1 2
main::(perldebug.loop.pl:4):        print qq[$k $v\n];
  DB<1> s
3 4
main::(perldebug.loop.pl:4):        print qq[$k $v\n];
  DB<1> v
1       #!/usr/bin/perl --
2:      my %f = ( 1 .. 10 );
3:      while(my($k,$v)=each%f){
4==>        print qq[$k $v\n];
5       }
6:      print "done\n";
  DB<1> c 5
Line 5 not breakable.
  DB<2> c 6
7 8
9 10
5 6
main::(perldebug.loop.pl:6):    print "done\n";
  DB<3> q