[root@centos7 ~]# du -h test.txt 
4.0K test.txt
[root@centos7 ~]# > test.txt 
[root@centos7 ~]# du -h test.txt 
0 test.txt

[root@centos7 ~]# du -h test.txt 
4.0K test.txt
[root@centos7 ~]# true > test.txt 
[root@centos7 ~]# du -h test.txt 
0 test.txt

[root@centos7 ~]# du -h test.txt 
4.0K test.txt
[root@centos7 ~]# cat /dev/null > test.txt 
[root@centos7 ~]# du -h test.txt 
 test.txt
###################################################
[root@centos7 ~]# echo "Hello World" > test.txt 
[root@centos7 ~]# du -h test.txt 
4.0K test.txt
[root@centos7 ~]# cp /dev/null test.txt 
cp：是否覆盖"test.txt"？ y
[root@centos7 ~]# du -h test.txt 
 test.txt
##################################################
[root@centos7 ~]# echo "Hello World" > test.txt 
[root@centos7 ~]# du -h test.txt 
4.0K test.txt
[root@centos7 ~]# dd if=/dev/null of=test.txt 
记录了0+0 的读入
记录了0+0 的写出
0字节(0 B)已复制，0.000266781 秒，0.0 kB/秒
[root@centos7 ~]# du -h test.txt 
 test.txt

[root@centos7 ~]# echo "Hello World" > test.txt 
[root@centos7 ~]# du -h test.txt 
4.0K test.txt
[root@centos7 ~]# echo -n "" > test.txt ==>要加上"-n"参数，默认情况下会"\n"，也就是回车符
[root@centos7 ~]# du -h test.txt 
0 test.txt

[root@centos7 ~]# du -h test.txt 
4.0K test.txt
[root@centos7 ~]# truncate -s 0 test.txt -s参数用来设定文件的大小，清空文件，就设定为0；
[root@centos7 ~]# du -h test.txt 
0 test.txt