为什么<<<$x删除换行符？
> cat <<<"A
B" # prints two lines (as expected)
A
B
> x="A
B"
> cat <<<"$x" # prints two lines (again, as expected)
A
B
> cat <<<$x # prints one line (..Why only one line!? I would expected two lines, or just "A", or error; Who's eating up the new line?)
A B
新行为何消失？方便<<<专用吗？
还有其他情况发生类似的事情吗？ （除<<<$var之外）
此处与新行无关：https://www.tldp.org/LDP/abs/html/x17837.html （如果相关：GNU bash，版本4.2.46（2）-发行版）