Why not just do this?

$query = qq(SELECT * FROM users WHERE userid = \'$username\');

$sth = $dbh->prepare($query);
$sth->execute;

if(($sth->fetchrow)[0]){
  print "$userName is a valid user \n";
  exit;
}
print "$userName is an invalid user \n";
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Tradez
"Never underestimate the predicability of stupidity"
- Bullet Tooth Tony, Snatch (2001)

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