CentOS echo

echo  与 引号 与 shell 的关系

# 引号具有保留赋值的内容，该例子中的换行符被保留。
[ root@VM-0-9-centos pts/3 2021-01-30/31@6 18:05:41 /Server/datas/downloads/script ] 
# a="a
 b
 a
 c
 b
 d"

# shell 接收是以空格来分隔，因为 $a 没有引号，所以被 shell 展开为多个参数【其中 换行符被删除，同时将参数之间的多个空格替换为一个空格】交给 echo 处理
[ root@VM-0-9-centos pts/3 2021-01-30/31@6 18:06:02 /Server/datas/downloads/script ] 
# echo $a
a b a c b d

[ root@VM-0-9-centos pts/3 2021-01-30/31@6 18:06:05 /Server/datas/downloads/script ] 
# echo "$a"
a
b
a
c
b
d

[ root@VM-0-9-centos pts/3 2021-01-30/31@6 18:06:12 /Server/datas/downloads/script ] 
# b=$(echo "$a" | sort | uniq)

[ root@VM-0-9-centos pts/3 2021-01-30/31@6 18:06:45 /Server/datas/downloads/script ] 
# echo $b
a b c d

[ root@VM-0-9-centos pts/3 2021-01-30/31@6 18:06:52 /Server/datas/downloads/script ] 
# echo "$b"
a
b
c
d

[ root@VM-0-9-centos pts/3 2021-01-30/31@6 18:09:59 /Server/datas/downloads/script ] 
# b="$(echo "$a" | sort | uniq)"

[ root@VM-0-9-centos pts/3 2021-01-30/31@6 18:10:07 /Server/datas/downloads/script ] 
# echo $b
a b c d

[ root@VM-0-9-centos pts/3 2021-01-30/31@6 18:10:12 /Server/datas/downloads/script ] 
# echo "$b"
a
b
c
d