echo命令

• 概述
  用于在shell中打印shell变量的值，或者直接输出指定的字符串。
• 选项
  -n：不进行换行
  -e：让转义符生效
  \n：换行
  \t：制表符
  STRING可使用引号，单引号和双引号都可用
  单引号：强引用，变量引用不执行替换
  ~]# echo '$SHELL'
  双引号：弱引用，变量引用会被替换
  ~]# echo "$SHELL"
  注意：变量引用的正规符号
  ${name}
• 实例

  [root@localhost ~]# echo how are you doing.How do you do?
  how are you doing.How do you do?
  [root@localhost ~]# echo -e "how are you doing.\tHow do you do?"
  how are you doing.  How do you do?
  [root@localhost ~]# echo -e "how are you doing.\nHow do you do?"
  how are you doing.
  How do you do?