my @arr= nv.txt;

my (%hash, $key, $val);

foreach (@arr) {
  $pre1="\$hash{$key}";   #previous key  of the loop
  $pre2=$val;              #previous value of the loop
  ($key, $val) = split (/:/,$_,2);
    if($pre1 eq "\$hash{$key}")  #if previous and current key same
   {
    $hash{$key}= $pre . '\n' . $val; #concatenate
    }
      $hash{key}=$val;
    print "\$hash{$key}={$vaal}\n";



}