tail(1posix) - copy the last part of a file
-c  number
       The  application  shall  ensure  that  the  number option-argument is a decimal integer whose sign
       affects the location in the file, measured in bytes, to begin the copying:

                                 Sign   Copying Starts
                                 +      Relative to the beginning of the file.
                                 -      Relative to the end of the file.
                                 none   Relative to the end of the file.

The origin for counting shall be 1; that is, -c +1 represents the first byte of the file, -c -1 the last.
-f     If the input file is a regular file or if the file operand specifies  a  FIFO,  do  not  terminate
       after  the  last  line of the input file has been copied, but read and copy further bytes from the
       input file when they become available. If no file operand is specified and  standard  input  is  a
       pipe,  the  -f option shall be ignored. If the input file is not a FIFO, pipe, or regular file, it
       is unspecified whether or not the -f option shall be ignored.
-n  number
       This option shall be equivalent to -c number, except the starting location in the  file  shall  be
       measured  in lines instead of bytes. The origin for counting shall be 1; that is, -n +1 represents
       the first line of the file, -n -1 the last.