You will read in a file supplied from the commandline (filename.ext,) and write/overwrite out a file which will be called (filename.ext.mng.)
This file will be essentially the same as the original file, but will have all characters on all lines the reverse of the original. For example:
The original file has:
could eat no fat.
could eat no lean.
The output file will look like:
.taf on tae dluoc
.nael on tae dluoc