

          fcntl handle [attribute value]
               This command either returns a list of various boolean
               attributes controlling access to a file or set or
               clears one of the boolean attributes.  If attribute and
               value are not specified, then the list of the
               attributes that are set are return. If an attribute is
               not set, then it will not be included in the list.  The
               following attributes maybe returned:

               RDONLY - The file is opened for reading only.

               WRONLY - The file is opened for writing only.

               RDWR - The file is opened for reading and writing.

               APPEND - The file is opened for append only writes.
               All writes will be forced to the end of the file.

               NDELAY - The file is to be accessed with non-blocking
               I/O.  See the read system call for a description of how
               it affects the behaviour of file reads

               CLEXEC - Close the file on an process exec.  If the
               execvp command or some other mechanism causes the
               process to exec, the file will be closed.

               NOBUF - The file is not buffered. If set, then there no
               stdio buffering for the file.

               LINEBUF - Output the file will be line buffered. The
               buffer will be flushed when a newline is written, when
               the buffer is full, or when input is requested.

               The APPEND, NDELAY, and CLEXEC attributes may be set or
               cleared by specifying the attribute name and a value 1
               to set the attribute and 0 to clear it.

               The NOBUF and LINEBUF attributes may only be set (a
               value of 1) and only one of the options may be set.
               Once set, they may not be cleared. Thees option should
               be set before any I/O operations have been done on the
               file.
