How to delete a newline if it is the last character in a file?

perl -pe 'chomp if eof' filename >filename2

or, to edit the file in place:

perl -pi -e 'chomp if eof' filename

^{[Editor's note: -pi -e was originally -pie, but, as noted by several commenters and explained by @hvd, the latter doesn't work.]}

This was described as a 'perl blasphemy' on the awk website I saw.

But, in a test, it worked.