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FD(4) Device Drivers Manual FD(4)

NAME

fd, stdin, stdout, stderrfile 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.
These devices may not be opened by processes which are tainted as a result of setuid or setgid behaviours, as documented in issetugid(2). In those cases, an error return will occur with errno set to EPERM.

FILES

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

SEE ALSO

tty(4)
May 31, 2007 OpenBSD-6.1