linux shell 单双引号区别

.sh  文件执行权限赋予    chmod ( -u  root  )-x  script.sh

单引号 无视变量   双引号 执行变量

例：

a1='phone'

a2='this is a ${a1}'

echo ${a2}

结果：  this is a ${a1}

a1='phone'

a2="this is a ${a1}"

echo ${a2}

结果：  this is a phone