Generic awk script to calculate average on any field through command line argument

Question

I want to write a generic awk script that can take as input a file and a field number (in that file) and give me the average value of that field in that file. I would use it something like this:

bash$ avg.awk 3 input.file
22
bash$ avg.awk 4 input.file
2001

Of course, I can write the script if I know which field (e.g., $3) I am going to average beforehand. That would be something like this:

//{tot+=$3; count++}
END{
    print tot/count;
}

But I want to be able to change the field I want to average through a command line option. Is that possible? Thanks!

Answer 1

This one will do what you want:

$ cat avg.awk
#!/usr/bin/env awk -f
# Calculate average, syntax: avg.awk field-number file
BEGIN { field = ARGV[1]; ARGV[1] = "" }
{ sum += $field }
END { print sum / NR }

$ cat data
1 5 7
3 6 5
8 4 6

$ avg.awk 1 data
4

$ avg.awk 2 data
5

$ avg.awk 3 data
6

Answer 2

{ tot += $field; count++ }
END { print tot/count }

call like awk -v field=3 -f avg.awk input.file