Inserting a New Column into a CSV File-CodePudding

I need to insert a new column in front of the first column in a CSV file. I'm trying to use an awk solution

CSV File

A,B,C,D,E,F
1,2,3,4,5,6
2,3,4,5,6,7
3,4,5,6,7,8
4,5,6,7,8,9

Attempted Code

awk 'BEGIN{FS=OFS=","}{$1=$1 OFS (FNR<1 ? $1 "0\n0\n0\n0" : "col")}1'

Expected Result

col,A,B,C,D,E,F
0,1,2,3,4,5,6
0,2,3,4,5,6,7
0,3,4,5,6,7,8
0,4,5,6,7,8,9

CodePudding user response：

One way could be to print col, if it's the first line and 0, if it's any of the other lines. Then print the rest of the columns:

awk 'NR==1 { printf("col,") } NR>1 { printf("0,") } { print }'

Broken down:

NR==1 {             # execute this block if it's the first line
    printf("col,")
}
NR>1 {              # execute this block if it's any other line
    printf("0,")
}
{                   # always execute this block
    print
}

CodePudding user response：

I would harness GNU AWK for this task following way, let file.csv content be

A,B,C,D,E,F
1,2,3,4,5,6
2,3,4,5,6,7
3,4,5,6,7,8
4,5,6,7,8,9

then

awk 'BEGIN{FS=OFS=","}{print NR==1?"col":"0", $0}' file.csv

gives output

col,A,B,C,D,E,F
0,1,2,3,4,5,6
0,2,3,4,5,6,7
0,3,4,5,6,7,8
0,4,5,6,7,8,9

Explanation: I inform GNU AWK that both field separator and output field separator is comma. For each line I print col if it is first row else 0 followed by whole line ($0).

(tested in gawk 4.2.1)