Print every nth column of a file

Question

I have a rather big file with 255 coma separated columns and I need to print out every third column only.

I was trying something like this

awk '{ for (i=0;i<=NF;i+=3) print $i }' file

but that doesn't seem to be the solution, since it prints to only one long column. Anybody can help? Thanks

Answer 1

Here is one way to do this.

The script prog.awk:

BEGIN {FS = ","} # field separator
{for (i = 1; i <= NF; i += 3) printf ("%s%c", $i, i + 3 <= NF ? "," : "\n");}

Invocation:

awk -f prog.awk <input.csv >output.csv

Example input.csv:

1,2,3,4,5,6,7,8,9,10
11,12,13,14,15,16,17,18,19,20

Example output.csv:

1,4,7,10
11,14,17,20