Shell Programming and Scripting

Hi,

Is their anyway to compare the value of a field in one line with the previous line?

I would like to

if previous volume name is the same then subtract the current value of $4 with the previous value of $4


data file

host date volume mb used
----------------------------------------------------
server1 02/01/2008 groups 10mb
server1 03/01/2008 groups 15mb
server1 04/01/2008 groups 20mb
server2 02/01/2008 users 50mb
server2 03/01/2008 users 75mb
server2 04/01/2008 users 100mb
server2 04/01/2008 users 125mb

what i would like the output to look like

host date volume mb used difference
--------------------------------------------------------------
server1 02/01/2008 groups 10mb 0
server1 03/01/2008 groups 15mb 5
server1 04/01/2008 groups 20mb 10
server2 02/01/2008 users 50mb 0
server2 03/01/2008 users 75mb 25
server2 04/01/2008 users 100mb 50
server2 04/01/2008 users 125mb 75

Any help would be greatly appreciated!

Thanks,
JD

Actually your requirement isn't quite as simple as you state it, because judging by your sample output you want to subtract it from the original value for that volume name, not just the previous one.

Try this:

Code:

awk '
        NR<3 { print; next } # print headings
        orig[$3]=="" { orig[$3]=int($4) }
        { print $0,int($4)-orig[$3] }
' inputfile

Note that this assumes the units will always be "mb".