The code structure you have is not designed for one print at the end. It's designed to step through a list of username/password pairs.

Tell us how you plan to use the code you've shown with the feature you're seeking, and we might give a better answer.

In the meantime, I'm guessing you want something like this:

open(TEMP,">$tmpfile") || die "Can't create $tmpfile.\n";
$found_user = 0; # flag
foreach $i (@indata)
{
  chomp($i);
  ($username,$password) = split(/\|/,$i);
  if ($username eq $in{'oldname'})
    {
     $found = 1;
     last;
    }
}
if (not $found)
  {
   print TEMP "Username $username is not registered\n";
  }
close(TEMP);
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Of course, I'm wondering where $in{'oldname'} and @indata come from, or even if they factor into the code your seeking.

OTOH, if you're looking to incorprate this behavior in your given code example, change the else to something like this (or perhaps insert this in front of it):

      elsif ($username eq $in{'oldname'})
           {
            $found = 1;
            last;
           }
[download]

(and keep the if (not $found) block).

You should probably add a last; to each of the if/elsif blocks, unless you're planning on doing something with every username in @indata.

-QM
--
Quantum Mechanics: The dreams stuff is made of