变量键盘读取和声明变量

read 【-pt】变量

    -p 后面可以加提示符

    -t 后面可以加秒数，限制等待时间r

declare/typeset [ ] 变量

    -a 声明变量为数组

    -i 整数数字

    -r 变量为只读

    -x 变量变成系统环境变量

[mao@localhost ~]$ bash

[mao@localhost ~]$ echo $sum

[mao@localhost ~]$ declare -x sum

[mao@localhost ~]$ bash

[mao@localhost ~]$ echo $sum

6

---

[mao@localhost ~]$ echo "${sum}"

6

[mao@localhost ~]$ echo $ {sum}

$ {sum}

[mao@localhost ~]$ echo ${sum}

6

[mao@localhost ~]$ echo $sum

6

---

数组a[i]

[mao@localhost ~]$ a[1]=1

[mao@localhost ~]$ a[2]=2

[mao@localhost ~]$ a[3]=3

[mao@localhost ~]$ echo $a[1]

[1]

[mao@localhost ~]$ echo "$a[1]"

[1]

[mao@localhost ~]$ echo ${a[1]}

1

[mao@localhost ~]$ echo "${a[1]}"

1

[mao@localhost ~]$ echo ${a[1]},${a[2]},${a[3]}     ____最保险

1,2,3