Suppose we have a text file contain a lot of blank lines like the example below :

tedy@tedy-laptop:~$ cat test
asia 

amerika 

afrika 

australia 

jakarta 

Indonesia

Sometime we need to remove all blank lines and grab only the text content. To do that we can use the awk utility :

tedy@tedy-laptop:~$ awk 'NF > 0' test
asia
amerika
afrika
australia
jakarta
Indonesia
tedy@tedy-laptop:~$

Another example, we have a text file like this :

tedy@tedy-laptop:~/Desktop$ cat test.txt
eth0      Link encap:Ethernet  HWaddr 00:17:42:bd:fc:f8
          inet addr:192.168.131.158  Bcast:192.168.131.255  Mask:255.255.255.0
          inet6 addr: fe80::217:42ff:febd:fcf8/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:554121 errors:0 dropped:2 overruns:0 frame:0
          TX packets:460920 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:440871435 (440.8 MB)  TX bytes:384609487 (384.6 MB)
          Interrupt:16 

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:81280 errors:0 dropped:0 overruns:0 frame:0
          TX packets:81280 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:77083351 (77.0 MB)  TX bytes:77083351 (77.0 MB) 

wlan0     Link encap:Ethernet  HWaddr 00:1f:3b:7e:a1:ef
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B) 

wmaster0  Link encap:UNSPEC  HWaddr 00-1F-3B-7E-A1-EF-00-00-00-00-00-00-00-00-00-00
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

We can remove all blank lines using grep utility :

tedy@tedy-laptop:~/Desktop$ cat test.txt | grep -v '^$'
eth0      Link encap:Ethernet  HWaddr 00:17:42:bd:fc:f8
          inet addr:192.168.131.158  Bcast:192.168.131.255  Mask:255.255.255.0
          inet6 addr: fe80::217:42ff:febd:fcf8/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:554121 errors:0 dropped:2 overruns:0 frame:0
          TX packets:460920 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:440871435 (440.8 MB)  TX bytes:384609487 (384.6 MB)
          Interrupt:16
lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:81280 errors:0 dropped:0 overruns:0 frame:0
          TX packets:81280 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:77083351 (77.0 MB)  TX bytes:77083351 (77.0 MB)
wlan0     Link encap:Ethernet  HWaddr 00:1f:3b:7e:a1:ef
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)
wmaster0  Link encap:UNSPEC  HWaddr 00-1F-3B-7E-A1-EF-00-00-00-00-00-00-00-00-00-00
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)
tedy@tedy-laptop:~/Desktop$