splitとundef

splitで、undefが来たり空文字列が来たりする。

$  perl -Mstrict

my ($s1, $s2, $s3)  = split(/=/, '=');

print defined $s1, " ← S1\n";

print defined $s2, " ← S2\n";

print defined $s3, " ← S3\n";
my @arr_s  = split(/=/, '=');

print defined $arr_s[0], " ← S[0]\n";

print defined $arr_s[1], " ← S[1]\n";

print scalar(@arr_s), " ← count\n";
【結果】

1 ← S1

1 ← S2

 ← S3

 ← S[0]

 ← S[1]

0 ← count

誰か解説求む。