while( my( $key, $value ) = each %db_stru ) {
    print "$key contains tables:\n";
    print "\t$_:" foreach @{$value};
}

##</code><code>##

while( my( $key, $value ) = each %db_stru ) {
    my $out = "$key contains tables:\n";
    $out .= "\t$_:" foreach @{$value};
    print "$out\n";
}

##</code><code>##

{
	local $" = ":\t";
	while( my( $key, $value ) = each %db_stru ) {
		print "$key contains tables:\n\t@{$value}\n"
	}
}