freebsd man page for dup3

DUP3(3) 						   BSD Library Functions Manual 						   DUP3(3)

NAME
     dup3 -- duplicate an existing file descriptor

LIBRARY
     Standard C Library (libc, -lc)

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

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

DESCRIPTION
     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).

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

ERRORS
     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.

SEE ALSO
     accept(2), close(2), dup2(2), fcntl(2), getdtablesize(2), open(2), pipe(2), socket(2), socketpair(2)

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

HISTORY
     The dup3() function appeared in FreeBSD 10.0.

BSD
								  August 16, 2013							       BSD