FD(4) BSD Kernel Interfaces Manual FD(4)

NAME
     ffdd, ssttddiinn, ssttddoouutt, ssttddeerrrr - 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, FDUPFD, 0);

     are equivalent.

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

           fd = fcntl(STDINFILENO,  FDUPFD, 0);
           fd = fcntl(STDOUTFILENO, FDUPFD, 0);
           fd = fcntl(STDERRFILENO, FDUPFD, 0);

     Flags to the open(2) call other than ORDONLY, OWRONLY and ORDWR are
     ignored.

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

SEE ALSO
     tty(4)

BSD                              June 9, 1993                              BSD