usr/share/man/cat4/stdout.0

FD(4)                       BSD Programmer's Manual                      FD(4)

N\bNA\bAM\bME\bE
     f\bfd\bd, s\bst\btd\bdi\bin\bn, s\bst\btd\bdo\bou\but\bt, s\bst\btd\bde\ber\brr\br - file descriptor files

D\bDE\bES\bSC\bCR\bRI\bIP\bPT\bTI\bIO\bON\bN
     The files _\b/_\bd_\be_\bv_\b/_\bf_\bd_\b/_\b0 through _\b/_\bd_\be_\bv_\b/_\bf_\bd_\b/_\b# 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 ex-
     isting descriptor, the call:

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

     and the call:

           fd = fcntl(0, F_DUPFD, 0);

     are equivalent.

     Opening the files _\b/_\bd_\be_\bv_\b/_\bs_\bt_\bd_\bi_\bn, _\b/_\bd_\be_\bv_\b/_\bs_\bt_\bd_\bo_\bu_\bt and _\b/_\bd_\be_\bv_\b/_\bs_\bt_\bd_\be_\br_\br 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.

F\bFI\bIL\bLE\bES\bS
     /dev/fd/#
     /dev/stdin
     /dev/stdout
     /dev/stderr

S\bSE\bEE\bE A\bAL\bLS\bSO\bO
     tty(4)

4.4BSD                           June 9, 1993                                1