linux下查找文件空行行号的方法

[root@mail ~]# cat aa.txt
hahahaha
aaaaaaa
aaaaaaa
bbbbbbbbbbbbb
vvvvvvvv
ddddddddd
vvvvvvvv
aaaaaaa
bbbbbbbbbbbbb
ddddddddddd
$
#
345
345
a5^
[root@mail ~]# sed -n '/[a-zA-Z0-9@#$%^&*]/!=' aa.txt
4

[root@mail ~]# grep -n ^$ aa.txt
4:
 
[root@mail ~]# awk '/^$/{print NR}' aa.txt
4
 
[root@mail ~]# sed -n '/^$/=' aa.txt
4