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FD(4)			    Kernel Interfaces Manual			 FD(4)

NAME
       fd, stdin, stdout, stderr -- file descriptor files

DESCRIPTION
       The  files  /dev/fd/0 through /dev/fd/# refer to	file descriptors which
       can be accessed through the file	system.	 If  the  file	descriptor  is
       open and	the mode the file is being opened with is a subset of the mode
       of the existing descriptor, the call:

	     fd	= open("/dev/fd/0", mode);

       and the call:

	     fd	= fcntl(0, F_DUPFD, 0);

       are equivalent.

       Opening the files /dev/stdin, /dev/stdout and /dev/stderr is equivalent
       to the following	calls:

	     fd	= fcntl(STDIN_FILENO,  F_DUPFD,	0);
	     fd	= fcntl(STDOUT_FILENO, F_DUPFD,	0);
	     fd	= fcntl(STDERR_FILENO, F_DUPFD,	0);

       Flags  to the open(2) call other	than O_RDONLY, O_WRONLY	and O_RDWR are
       ignored.

IMPLEMENTATION NOTES
       By default, /dev/fd is provided by devfs(5), which provides  nodes  for
       the first three file descriptors.  Some sites may require nodes for ad-
       ditional	 file  descriptors;  these  can	 be made available by mounting
       fdescfs(5) on /dev/fd.

FILES
       /dev/fd/#
       /dev/stdin
       /dev/stdout
       /dev/stderr

SEE ALSO
       tty(4), devfs(5), fdescfs(5)

FreeBSD	14.3			 June 9, 1993				 FD(4)

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