[SOLVED] Make CSV empty commas into "dittos" of previous line's items

Issue

I have a file where the first line is the header of the file and corresponding values are present in the subsequent rows. I want to replace the 3rd line of commas with the values of the 2nd line. So my 3rd line will contain values of 2nd line plus existing values of the 3rd line. And this process continues till I get again a line with similar pattern values and it should be copied to subsequent rows to produce a result like 3rd line.

Programming language: Unix shell scripting

E.g. sale.txt

Name,flavour,country,sale,POC
Magnum,chocolate,UK
,,,100,Alex
,,,200,Aman
,,,50,Perish
Cornetto,vanilla,US
,,,30,Robert
,,,60,Mary
.
.
.

Output should be:

Name,flavour,country,sale,POC
Magnum,chocolate,UK,100,Alex
Magnum,chocolate,UK,200,Aman
Magnum,chocolate,UK,50,Perish
Cornetto,vanilla,US,30,Robert
Cornetto,vanilla,US,60,Mary
.
.
.

Solution

I created an awk script for this:

ans.sh

#!/usr/bin/awk -f

BEGIN   { OFS = FS = "," }

NR > 1 {
    if ($1 == "") $1 = Name
    if ($2 == "") $2 = flavour
    if ($3 == "") $3 = country

    Name = $1
    flavour = $2
    country = $3
       }

{ print }

Then I ran this script on your file:

mayankp@mayank:~/Documents$ awk -f ans.sh sale.txt 
Name,flavour,country,sale,POC
Magnum,chocolate,UK
Magnum,chocolate,UK,100,Alex
Magnum,chocolate,UK,200,Aman
Magnum,chocolate,UK,50,Perish
Cornetto,vanilla,US
Cornetto,vanilla,US,30,Robert
Cornetto,vanilla,US,60,Mary

Hope this helps.

Answered By - Mayank Porwal