sunos man page for fd

fd(4)								   File Formats 							     fd(4)

NAME
       fd - file descriptor files

DESCRIPTION
       These files, conventionally called  /dev/fd/0, /dev/fd/1, /dev/fd/2, and so on, refer to files accessible through file descriptors. If file
       descriptor  n is open, these two system calls have the same effect:

       fd = open("/dev/fd/n",mode);
       fd = dup(n);

       On these files  creat(2) is equivalent to open, and mode is ignored. As with  dup, subsequent reads or writes on  fd fail unless the origi-
       nal file descriptor allows the operations.

       For convenience in referring to standard input, standard output, and standard error, an additional set of names is provided:  /dev/stdin is
       a synonym for  /dev/fd/0, /dev/stdout for /dev/fd/1, and /dev/stderr for  /dev/fd/2.

SEE ALSO
       creat(2), dup(2), open(2)

DIAGNOSTICS
       open(2) returns -1 and  EBADF if the associated file descriptor is not open.

SunOS 5.10							    3 Jul 1990								     fd(4)