use DBI;

my $dbh=DBI->connect('dbi:Pg:dbname=template1', 'user' , 'password', { RaiseError => 1, AutoCommit => 1 } );

# [...]

sub pg_drop_if_exists {
  my $dbname = shift;
  my $sth = $dbh->prepare(q{SELECT datname FROM pg_catalog.pg_database WHERE datname = ?});
  $sth->execute($dbname);

  if ($sth->fetchrow_arrayref()) {
    $dbh->do('DROP DATABASE ' . $dbname); #placeholder and quote don't work, security!
  }
}

pg_drop_if_exists('nikos_db');