How to debug in Perl ?

If it is a small program,you can use this way:

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C:Rebeccascriptperl>perl -d calculate.pl

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Loading DB routines from perl5db.pl version 1.39_10

Editor support available.

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

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main::(calculate.pl:3): my $number1 = 10;

? DB<1> $number1= 3?? #you can change the number here

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? DB<2> n #press n to execute next command

main::(calculate.pl:4): my $number2 = 6;

? DB<2> print$number1 # but you can see it didn’twork

10

? DB<3> $number1= 3 #change it again here,it willwork!!

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? DB<4> print$number1 #see,it worked.

3

? DB<5> n

main::(calculate.pl:5): my $sum = $number1 + $number2;

? DB<5> print$number2

6

? DB<6> $number= -1 # I wanted to change number2 aswell,but I just type number by mistake….

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? DB<7> n

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

? DB<7> print$sum

9?

? DB<8> q #quit the debug now