How to debug in Perl?

If It is a small program, you can use the this to:

c:\rebecca\script\perl>perl-d calculate.pl

Loading DB routines from perl5db.pl version 1.39_10

Editor support available.

Enter h or ' h ' for help, or ' Perldoc perldebug ' for morehelp.

Main::(Calculate.pl:3): my 1 = 10;

Db<1> 1= 3 #you can change the number here

db<2> n #press N to execute next command

Main::(calculate.pl:4): my 2 = 6;

Db<2> Print1 # But you can see it didn ' twork

10

Db<3> 1= 3 #change It again here, it willwork!!

db<4> print1 #see, it worked.

3

db<5> N

Main::(calculate.pl:5): My $sum = 1 + 2;

Db<5> Print2

6

db<6> = 1 # I wanted to the change number2 aswell, but I just type number by mistake ....

db<7> N

Main::(calculate.pl:7): print $sum, "\ n";

Db<7> Print$sum

9

db<8> q #quit the debug now

How to debug in Perl?