That works. But only because you have two errors that (fortuitously) pretty much cancel each other out.

sub new()
{
        my $self={};
        $self->{FORM_VAR}=undef;
        bless($self);
        return $self;
}
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You should always use the two-argument version of bless. Your constructor should look like this:

sub new {
  my $class = shift;
  my $self = {};
  # some initialisation
  bless($self, $class);
  return $self;
}
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But that doesn't work here because you have this:

my $obj = main::new();

You're calling new() as a function, not as a class method, so it doesn't get passed the class name.

You should invoke the constructor as a class method.

my $obj = main->new();
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Perl doesn't strictly differentiate between functions and methods. But the programmer should.