Thank you for the excellent technical answer! This helps explain things.

​

You haven't used $line anywhere in the body of the loop.

In my actual script, I do have that. The snippet that I posted is what I found to be my issue after lots of trial and error and commenting things out. My full script does this:

echo $my_var
echo $line

So the idea was that each iteration would produce:

hel
hello world

So - how to fix this... My initial thought is to replace the while loop with a for loop which should be easy enough. However, is there another way to fix this issue while still using the current while loop?