In Unix, what do I do when a file I want to edit in vi says "Line too long"?

In Unix, when the vi editor says “line too long” it’s usually because it was copied up from a Mac where the end of line marker is different.

This command works for me on Solaris:

tr '\015' '\012' < in_file > out_file

Source: http://www.maths.ox.ac.uk/help/faqs/files/dos-mac-to-unix.shtml

The numbers are in octal. Be sure and transpose from decimal or hex if necessary.