Padding columns of csv - bash

Question

I have a csv file which contains a large number of csv seperated lines of data. i want to find the maximum length of the line then need to print NO in a new column
file.csv
1,2,3,4,
1,4,7,8,9,10,11,13
1,2,
1,1,2,4,5,6,7,8,9,10,11
abc,def,ghi,jkl
expected result
1,2,3,4,,,,,,,,,,,,,,,,N0
1,4,7,8,9,10,11,13,,,,,NO
1,2,,,,,,,,,,,,,,,,,,,,NO
1,1,2,4,5,6,7,8,9,10,1,NO
abc,def,ghi,jkl,,,,,,,,NO
cat file | cat > file.csv
echo "N0" >> file.csv
output obtained
1,2,3,4,NO
1,4,7,8,9,10,11,13,NO
1,2,NO
1,1,2,4,5,6,7,8,9,10,11,NO
abc,def,ghi,jkl,NO

Answer 1

You need to read the file twice, once to get the maximum number of columns, once to print the output:
awk -F, 'NR==FNR{if(m<=NF)m=NF;next} # Runs only on first iteration
{printf "%s",$0;for(i=0;i<=(m-NF);i++)printf ",";print "NO"}' file file
filename twice -----^
Output (12 columns in each row):
1,2,3,4,,,,,,,,NO
1,4,7,8,9,10,11,13,,,,NO
1,2,,,,,,,,,,NO
1,1,2,4,5,6,7,8,9,10,11,NO
abc,def,ghi,jkl,,,,,,,,NO

Answer 2

It's hard to imagine why you'd want to pad the lines with commas so here's what I think you really want which is to make every line have the same number of fields:
$ awk 'BEGIN{FS=OFS=","} NR==FNR{m=(m>NF?m:NF);next} {$(m+1)="NO"} 1' file file
1,2,3,4,,,,,,,,NO
1,4,7,8,9,10,11,13,,,,NO
1,2,,,,,,,,,,NO
1,1,2,4,5,6,7,8,9,10,11,NO
abc,def,ghi,jkl,,,,,,,,NO
and here's what you said you want anyway:
$ awk '{n=length()} NR==FNR{m=(m>n?m:n);next} {p=sprintf("%*s",m-n+1,""); gsub(/ /,",",p); $0=$0 p "NO"} 1' file file
1,2,3,4,,,,,,,,,,,,,,,,,NO
1,4,7,8,9,10,11,13,,,,,,NO
1,2,,,,,,,,,,,,,,,,,,,,,NO
1,1,2,4,5,6,7,8,9,10,11,NO
abc,def,ghi,jkl,,,,,,,,,NO

Answer 3

awk -F, 'BEGIN{m=0}
{if(NF>m)m=NF;ar[NR]=$0;ars[NR]=NF;}
END{for(i=1;i<=NR;i++)
{for(j=ars[i];j<m;j++){ar[i]=ar[i]","}ar[i]=ar[i]"NO";
print ar[i]}}' <<<'1,2,3,4,
1,4,7,8,9,10,11,13
1,2,
1,1,2,4,5,6,7,8,9,10,11,12
abc,def,ghi,jkl
a,b'
output:
1,2,3,4,,,,,,,,NO
1,4,7,8,9,10,11,13,,,,NO
1,2,,,,,,,,,,NO
1,1,2,4,5,6,7,8,9,10,11,12NO
abc,def,ghi,jkl,,,,,,,,NO
a,b,,,,,,,,,,NO
if lines must be have same size:
awk -F, 'BEGIN{m=0}
{if(length($0)>m)m=length($0);ar[NR]=$0;ars[NR]=length($0);}
END{for(i=1;i<=NR;i++)
{for(j=ars[i];j<m;j++)
{ar[i]=ar[i]","}ar[i]=ar[i]"NO";
print ar[i]}}' <<<'1,2,3,4,
1,4,7,8,9,10,11,13
1,2,
1,1,2,4,5,6,7,8,9,10,11,12
abc,def,ghi,jkl
a,b'
output:
1,2,3,4,,,,,,,,,,,,,,,,,,,NO
1,4,7,8,9,10,11,13,,,,,,,,NO
1,2,,,,,,,,,,,,,,,,,,,,,,,NO
1,1,2,4,5,6,7,8,9,10,11,12NO
abc,def,ghi,jkl,,,,,,,,,,,NO
a,b,,,,,,,,,,,,,,,,,,,,,,,NO
if you want also comma after max length line run for loop until m+1;