Input 2 files, calculate diffs line by line

Shell Programming and Scripting
1

Hi

I am new to Unix and need help with the following (to you all I'm sure) simple task. I am trying to output the differences between previous snaphots of various filesystem sizes to the present sizes.

I have three files (e.g.) :

file 1 file 2 file 3
10 100 /var
20 200 /opt
300 30 /tmp

I need a script to subtract the respective fields of file1 & file2, match this up with the respective fields in file3 and to output the result of this to standard output line by line.

i.e. Filesystem /var has changed by 90Kb
Filesystem /opt has changed by 180KB
Filesystem /tmp has changed by 270KB

I have tried :

#!/bin/ksh
for filesystem in `cat filesystems`
do
for curr_fs in `cat curr_fs_sizes`
do
for prev_fs in `cat prev_fs_sizes`
do
change=`expr ${curr_fs} - ${prev_fs}`
echo "Filesystem ${filesystem} has changed by ${change}Kb"
done
done
done

which cycles through every file 3 times each :frowning:

Any help greatly appreciated folks ! :frowning:

2

If I have understood your requirement properly, this is what you can do...

paste file1 file2 file3 > newfile
awk '{printf("Filesystem %s has changed by %d Kb.\n",$3,$2-$1)}' newfile
3

Not what I was expecting rakeshawasthi ! But it does of course work. Many thanks for taking the trouble to reply to me.

4

Assuming the given files have the same number of records, you can do it in one command,

awk '{ if((getline v1 < f1)>0 && (getline v2 < f2)>0)
       print "Filesystem " $0 " has changed by " (v1>v2?v1-v2:v2-v1)"Kb"
     } ' f1="./file1" f2="./file2" file3

Output:

Filesystem /var has changed by 90Kb
Filesystem /tmp has changed by 180Kb
Filesystem /opt has changed by 270Kb
5

yes that works too - thank you rubin