もくもく

my $str = "string";
substr($str,0,0,"string");

print $str;

my $str = "string";
$str = $str."string";

print $str;

my $count = 0;
my $str = "";

while($count < 10){
	$str = $str."$count";
	$count++;
}

print $str;

my $count = 0;
my $str = "";

until($count > 9){
	$str = $str."$count";
	$count++;
}

print $str;

untilってどうも使いづらい気がする。どんなときに使えばいいんだろう？