The new constructor code needs a class parameter like this

{package Student;
  sub new {
    my ($class, $name, $age, $regd_no)=@_;
    my $objref = { NAME    => $name, 
                   AGE     => $age,
                   REGD_NO => $regd_no
                 };
    print"\n class: $class\n";           
    return bless $objref, $class;
  }

  ...
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and the text file needs to be opened again to read the file a second time

...
my @students;
open (DNAFILE, '<', $DNAfilename) or die "Perl says $!"; 
while (<DNAFILE>) {
  chomp; 
  push @students, Student->new(split /:/);
} 
...
[download]

poj