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@(#)fd.4 8.1 (Berkeley) 6/9/93
$FreeBSD$
.Dd June 9, 1993 .Dt FD 4 .Os .Sh NAME .Nm fd , .Nm stdin , .Nm stdout , .Nm stderr .Nd file descriptor files .Sh DESCRIPTION The files
a /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: d -literal -offset indent fd = open("/dev/fd/0", mode); .Ed
p and the call: d -literal -offset indent fd = fcntl(0, F_DUPFD, 0); .Ed
p are equivalent.
p Opening the files
a /dev/stderr is equivalent to the following calls: d -literal -offset indent fd = fcntl(STDIN_FILENO, F_DUPFD, 0); fd = fcntl(STDOUT_FILENO, F_DUPFD, 0); fd = fcntl(STDERR_FILENO, F_DUPFD, 0); .Ed
p Flags to the .Xr open 2 call other than .Dv O_RDONLY , .Dv O_WRONLY and .Dv O_RDWR are ignored. .Sh IMPLEMENTATION NOTES By default,
a /dev/fd is provided by .Xr devfs 5 , which provides nodes for the first three file descriptors. Some sites may require nodes for additional file descriptors; these can be made available by mounting .Xr fdescfs 5 on
a /dev/fd . .Sh FILES l -tag -width /dev/stderr -compact t Pa /dev/fd/# t Pa /dev/stdin t Pa /dev/stdout t Pa /dev/stderr .El .Sh SEE ALSO .Xr tty 4 , .Xr devfs 5 , .Xr fdescfs 5