4、在根目录下建立user子目录，在该目录下分别建立user1、user2、user3子目录，利用touch命令分别在对应的目录下建立测试文件，测试文件名为user1.txt、user2.txt、user3.txt。将/user/user1/user1.txt文件复制到/mnt目录下，删除/user/user3子目录
cd /
mkdir user/user1 user/user2 user/user3
touch /user/user1/user1.txt /user/user2/user2.txt /user/user3/user3.txt
mv /user/user1/user1.txt /mnt
cd /
mkdir -p user/user1
mkdir -p user/user2
mkdir -p user/user3
touch user/user1/user1.txt
touch user/user2/user2.txt
touch user/user3/user3.txt
cp /user/user1/user1.txt /mnt
rm -f /user/user3/*