you are talking about the debugger?

It doesn't execute anything before you don't type any stepping commands like n.

try h for help and plz read the docs.

UPDATE:

lanx@nc10-ubuntu:/tmp$ cat >tst.pl
$|=1;
for (1..10) { 
   print "$_\n";
}
lanx@nc10-ubuntu:/tmp$ perl -d tst.pl
 
Loading DB routines from perl5db.pl version 1.3
Editor support available.
 
Enter h or `h h' for help, or `man perldebug' for more help.
 
main::(tst.pl:1):    $|=1;
  DB<100> n
main::(tst.pl:2):    for (1..10) { 
  DB<100> n
main::(tst.pl:3):       print "$_\n";
  DB<100> n
1
main::(tst.pl:3):       print "$_\n";
  DB<100> n
2
main::(tst.pl:3):       print "$_\n";
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EDIT: last paragraph erased.