NAME

dup3 —

duplicate an existing file descriptor

LIBRARY

Standard C Library (libc, -lc)

#include <fcntl.h>
#include <unistd.h>

int
dup3(int oldd, int newd, int flags);

The dup3() function duplicates an existing object descriptor while allowing the value of the new descriptor to be specified.

The close-on-exec flag on the new file descriptor is determined by the O_CLOEXEC bit in flags.

If oldd ≠ newd and flags == 0, the behavior is identical to dup2(oldd, newd).

If oldd == newd, then dup3() fails, unlike dup2(2).

The value -1 is returned if an error occurs. The external variable errno indicates the cause of the error.

The dup3() function fails if:

[EBADF]: The oldd argument is not a valid active descriptor or the newd argument is negative or exceeds the maximum allowable descriptor number
[EINVAL]: The oldd argument is equal to the newd argument.
[EINVAL]: The flags argument has bits set other than O_CLOEXEC.

The dup3() function does not conform to any standard.

The dup3() function appeared in FreeBSD 10.0.