Shell Programming and Scripting

Hello everyone,

I had such a helpful and quick response last time and it worked so perfectly, perhaps someone can help me with this problem I have (once again this is for research and not a homework problem). For instance, I have a file (varying numbers of rows, etc) with three columns of data in each row:

11 20 180
13 55 180
10 75 360
20 15 400

I would like a very small script (using awk preferably, but bash works too) that prints a fourth column that keeps track of the running difference between the value of the third column on each row. So, the output would look something like this:

11 20 180 0
13 55 180 0
10 75 360 180
20 15 400 220

The 4th column on the first row would be zero since it is the start of the file. The value for the 3rd column didn't change on the second row, so the 4th column is zero again for the second row. The value of the 3rd column changed by 180 from the second row to the third row, so 180 is printed. On the fourth row, the 3rd column value changed by 40, so that number is added to 180 from the 4th row of the 3rd column, and 220 is printed. This needs to continue on down until the end of the file.

Any and all help would be most appreciated. Thank you very much for helping me further my computer programming learning skills!

Try this:

Code:

awk -va=0 -vb=0 '{if (NR!=1) {b=b+$NF-a}; if (NR==1) {print $0,b} else {print $0,b}; a=$NF;}' file.txt

---------- Post updated at 06:19 PM ---------- Previous update was at 06:17 PM ----------

I just saw that the if statement is actually redundant, so this makes more sense:

Code:

awk -va=0 -vb=0 '{if (NR!=1) {b=b+$NF-a};  {print $0,b}; a=$NF}' file.txt

Thanks for the help with the code! It does exactly what I want it to. I appreciate the assistance!