in reply to
Re^2: Pulling out data from one file thats not in another
in thread Pulling out data from one file thats not in another
There are already several tools to achieve what you want, writing your own is probably needless.
A standard Unix-like solution (works under bash):
$ diff <( sort master ) <( sort completed ) | grep '^<' | cut -d ' ' -
Depending on your needs you may want to use sort -u instead of a simple sort.
Or if you're under some Debian-derivative distro just install the moreutils package and use combine:
$ combine master not completed
Hope that helps.