Using GNU Parallel on Linux

Sometime ago I had created a C/C++ program to find the LAN machine/IP that is powered ON or OFF in our Departmental Computing Facility[DCF]. The local IPs have changed now.

The important thing was that program pings each machines/IP address one after another. It would take a lot of time. Recently, I have seen a cmd/package called parallel  that does it in one line linux command. Cool. I can add this to my bashrc which would need only 3 key stokes to find what I wanted.

If it is not installed already, do it

$ sudo apt-get install parallel


$ parallel --halt now,success=1 ping -c1 10.21.225.{1}{2} ::: 0 1 2 ::: 1 2 3 4 5 6 7 8 9 0

This is the one line cmd. Lets break it down and see what it says.

$ parallel echo {1}{2} ::: 0 1 2 ::: 1 2 3 4 5 6 7 8 9 0

what does the above command do. Prints all the numbers from 00 to 29. i.e echo 30 times.

echo 00
echo 01
...
echo 29

parallel does the same, but the order is immaterial.

But, to my purpose I used to check $? whether  0 or 1 or something in my old script. This is done smarter here.

--halt now,success=1 means stop running jobs even if one job is succeeded. WOW!


$ parallel --halt now,success=1 ping -c1 10.21.225.{1}{2} ::: 0 1 2 ::: 1 2 3 4 5 6 7 8 9 0 > /dev/null

I use the above line which prints only the IP I wanted. YAY!
Tata. See you.