I'll call it a week now - it's 17:37 over here. I'll pick up again on monday.

cheers Guys

The syntax looks correct. By the error message you are getting and the fact that you said this was in a script (not just on the command line) I suspect that there is a spurious, non-printable character in your script that is hosing up the scanning of the line properly and causing it to think that

Try this:
a. you can often find these non-printable chars by using "od -c filename | less"
b. re-type in the command on a new line and delete the old line altogether

Here is an example of how I reproduced your error. Look closely at the output of 'od -c' where there is actually a bad char (002 == CNTL-B) that your editor may not show you, but truly throws an error for nawk:

I checked. There are no hidden characters. For double measure, I have re-typed that line of code (not copied and pasted). Still the same error.

Finally resolved.

nawk -F"," -v red="$random_variable" '{print $red}' $w_dir/$file_name > $w_dir/${column_name}

The double-quotes around the variable did it.