Synopsis:
   $eof(<file descriptor>)

Technical:
   This function tests whether the client is currently at the end of the
   file pointed to by the given file descriptor.  The only valid input is
   a file descriptor returned by the $open() function.

Practical:
   This function is used to see if the end of a file has been reached.
   This is mostly useful while reading a file, such that it can be closed
   once the end is reached.

Returns:
   -1   error, no such file descriptor
    0   not at end of file
    1   end of file reached

See also:
   close(6); open(6); read(6)