use CGI qw(-debug);

##</code><code>##

use CGI qw(-debug);
use strict;
use warnings;

my $cgi = CGI->new;
print $cgi->param('a');

##</code><code>##

perl -d a.pl

##</code><code>##

perl -d a.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::(a.pl:5): my $cgi = CGI->new;
                                                                                                                                                               DB<1> n
(offline mode: enter name=value pairs on standard input; press ^D or ^Z when done)
a='a
b
v
d'
main::(a.pl:6): print $cgi->param('a');
                                                                                                                                                               DB<1> p $cgi->param('a')
a b v d
                                                                                                                                                               DB<2> q