Synopsis:
   $read(<fd> [<length>])

Technical:
   This function is used to read data from a file pointed to by the given
   file descriptor.  The file descriptor is returned when the file is
   opened for reading with the $open() function.  If a second argument is
   passed, that many bytes are read and returned; otherwise, it reads up
   to the next newline.

Practical:
   This function is the general-purpose interface to reading file contents.
   The normal usage is to just read a file line by line.  However, since
   you can also read an arbitrary number of bytes, it can also be used to
   read binary files (finding a use for this is left as an exercise for the
   user).

Returns:
   data read from file, or nothing on error

Examples:
   $read(4)                           returns next line from fd 4
   $read(4 30)                        returns next 30 bytes from fd 4

See Also:
   close(6); open(6); randread(6)