June 9, 1993 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.

### FILES

```/dev/fd/#`
```/dev/stdin`
```/dev/stdout`
```/dev/stderr`

### SEE ALSO

tty(4)