awk printing out an associative array with OFS

Question

I have the following awk code. It first determines the field numbers of interest in the header line and then it prints the output of those fields. The issue is that I am using an associative array to keep the field numbers of interest and thus I print out in the for loop and not using print but rather printf. Its problem is that it adds the separator also at the end of the line.

Is there any simple way around this (without e.g. running through the output again and removing the additional separators)? Or is there a better way to print out the fields the numbers of which are stored in an array?

awk '
    BEGIN {
        FS = ","; OFS = ","
        no_headers = 2; headers[1] = "header1"; headers[2] = "header3"
        k = 0
    }

    NR==1 {
        for (i=1; i<=no_headers; i++) {
            for (j=1; j<=NF; j++) {
                s = gensub(/"/, "", "g", $j)
                if (s==headers[i]) { col_no[++k] = j }
            }
        }
    }

    NR>1 {
        for (i=1; i<=k; i++) { printf "%s,", $col_no[i] }
        print ""
    }' test_awk.txt

a test file looks like this

"header1","header2","header3","header4"
"a","b","c",4
1,"b",,"d"
"a","2","c","d"

and my output at present looks like this

"a","c",
1,,
"a","c",

but I want it to look like this (i.e., no trailing delimiters)

"a","c"
1,
"a","c"

Answer 1

Modify your printf() statement to remove the , from the format specifier and add it inside the {..} part. Use a ternary operator to append the , if not for the last field

printf "%s", (i==k) ? $col_no[i] : $col_no[i]","