Well, to answer my own question, the "printf" method *does* work - it only appeared not to work becuase I got awk_filter.tmp files mixed up and I was using the 'print' version not the 'printf'...
In a loop, I want to append some text to a file without generating a new line (and then force a new line before re-iterating the loop). In the code below the first 'echo' command is OK as it uses...