       1mfcntl 4m22mfileId24m 4mattribute24m 4m?value24m?
              This  command either sets or clears a file option or returns its
              current value.  If 4mvalue24m is  not  specified,  then  the  current
              value  of  1mattribute  22mis returned.  All values are boolean. Some
              attributes maybe only be gotten, not  modified.   The  following
              attributes may be specified:

       1mRDONLY 22mThe file is opened for reading only. (Get only)

       1mWRONLY 22mThe file is opened for writing only.  (Get only)

       1mRDWR   22mThe file is opened for reading and writing.  (Get only)

       1mREAD   22mIf the file is readable. (Get only).

       1mWRITE  22mIf the file is writable. (Get only).

       1mAPPEND 22mThe  file  is opened for append-only writes.  All writes will be
              forced to the end of the file. (Get or set).

       1mNONBLOCK0m
              The file is to be accessed with non-blocking I/O.  See the  1mread0m
              system  call for a description of how it affects the behavior of
              file reads.

       1mCLOEXEC0m
              Close the file on an process exec.  If the 1mexecl 22mcommand or some
              other  mechanism causes the process to do an exec, the file will
              be closed if this option is set.

       1mNOBUF  22mThe file is not buffered. If set, then there  no  buffering  for
              the file.

       1mLINEBUF0m
              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.

       1mKEEPALIVE0m
              Keep  a socket connection alive.  If SIGPIPE is enabled, then it
              is sent if connection is broken  and  data  is  written  to  the
              socket.   If  SIGPIPE  is  ignored,  an error is returned on the
              write.  This attribute is valid only on  sockets.   By  default,
              SIGPIPE is ignored in Tcl.

              The  1mNONBLOCK22m,  1mNOBUF 22mand 1mLINEBUF 22mare provided for compatibility
              with older scripts.  The1mfconfigure 22mcommand is  preferred  method
              of getting and setting these attributes.

              The 1mAPPEND 22mand 1mCLOEXEC 22moptions are not available on 1mWindows22m.
