path1=$(cd `dirname $0`;pwd) #cd `dirname $0`;pwd 先cd到當前路徑然后pwd，打印成絕對路徑
path2=$(dirname $0) #dirname $0 只是獲取的當前腳本的相對路徑
path3=$(dirname $(readlink -f "$path")) #readlink -f $path 如果$path沒有鏈接，就顯示自己本身的絕對路徑
path4=$(dirname $PWD) #返回腳本文件的父目錄
echo ${path1}
echo ${path2}
echo ${path3}
echo ${path4}