Question

I have the following script

awk '{printf "%s", $1"-"$2", "}' $a >> positions;

where $a stores the name of the file. I am actually writing multiple column values into one row. However, I would like to print a comma only if I am not on the last line.

Answer 1

I would do it by finding the number of lines before running the script, e.g. with coreutils and bash:

awk -v nlines=$(wc -l < $a) '{printf "%s", $1"-"$2} NR != nlines { printf ", " }' $a >>positions

If your file only has 2 columns, the following coreutils alternative also works. Example data:

paste <(seq 5) <(seq 5 -1 1) | tee testfile

Output:

1   5
2   4
3   3
4   2
5   1

Now replacing tabs with newlines, paste easily assembles the date into the desired format:

 <testfile tr '\t' '\n' | paste -sd-,

Output:

1-5,2-4,3-3,4-2,5-1