标题环境的分割返回最后一个值 (Slices in scalar context return the last item of the slice. )
($t)=qw/"a","b"/;#个数不匹配,$t匹配"a"
$t=qw/"a","b"/;#此时$t=后一个
my@a=qw/firstsecondthird/;
my%h=(first=>'A',second=>'B');
my$t=@a[0,1]; #$tisnow'second'
my$u=@h{'first','second'}; #$uisnow'B'