https://www.cnblogs.com/37yan/p/6962563.html
caution!!! if should be end with fi
caution!!! there should be a space between [ and ! , also between 1 and ]
if [ ! $# -eq 1 ];then
#!/bin/bash
# 判断传入的参数的个数是不是一个
if [ ! $# -eq ];then
echo param error!
exit
fi # 判断目录是不是已经存在，如果不存在则创建，存在则输出“dir exist”
dirname=$
echo "the dir name is $dirname"
if [ ! -d $dirname ];then
mkdir $dirname
else
echo dir exist
fi