test

##### 变量
    声明: name="zhangsan"
    使用: echo ${name}  || echo $name
    只读: readonly name
    删除: unset name
    获取长度: echo ${#name} 

##### 字符串

##### 数组
    colors=(red blue pink yellow)
    echo ${colors[@]}

#!/bin/bash
userId="410221199411268412"
readonly userId
year=${userId:6:4}
programmingLanguage="Shell" 
languageLen=${#programmingLanguage}
echo "userId:${userId},在${year}年出生"
echo "programming language:${programmingLanguage} length:${languageLen}"
echo "current script file:$0"
echo $((100/2))


if [ -f test.txt ]
then
    [ -f test.txt ] && echo '-f true1'
else
    touch test.txt
    [ -f test.txt ] && echo '-f true2'
fi
# [ -d shell ] && echo '-d true1'
# mkdir shell
# [ -d shell ] && echo '-d true2'