eol copies infile to outfile, replacing every NL (Newline) by CR+NL (Carriage-Return followed by Newline).
NL is end-of-line in Unix text files. CR+NL are end-of-line in MS-DOS and OS/2 text files.
eol is smart enough not to change CR+NL to CR+NL+NL (i.e. detects when the input already has DOS style end-of-lines).
If you don't specify logfile, eol writes error messages to standard error.
-u2d : Replace every NL by CR+NL (default).
-d2u : Replace every CR+NL by NL. (No, eol does not remove every CR blindly - only when followed by a NL.)
-v : Print version banner and usage info to standard error (or logfile, if given), then exit.