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:
Jack Spratt
could eat no fat.
His wife
could eat no lean.
The output file will look like:
ttartpS kcaJ
.taf on tae dluoc
efiw siH
.nael on tae dluoc