-f    Follow. If the input-file is not a pipe,  the  program
           will  not  terminate  after the line of the input-file
           has been copied,  but  will  enter  an  endless  loop,
           wherein  it  sleeps  for a second and then attempts to
           read and copy further  records  from  the  input-file.
           Thus  it  may  be used to monitor the growth of a file
           that is being written by some other process.