DUP2(3C) Standard C Library Functions DUP2(3C)


NAME


dup2, dup3 - duplicate an open file descriptor

SYNOPSIS


#include <unistd.h>

int dup2(int fildes, int fildes2);


int dup3(int fildes, int fildes2, Bint flags);


DESCRIPTION


The dup2() function causes the file descriptor fildes2 to refer to the
same file as fildes. The fildes argument is a file descriptor referring
to an open file, and fildes2 is a non-negative integer less than the
current value for the maximum number of open file descriptors allowed
the calling process. See getrlimit(2). If fildes2 already refers to an
open file, not fildes, it is closed first. If fildes2 refers to fildes,
or if fildes is not a valid open file descriptor, fildes2 will not be
closed first.


The dup2() function is equivalent to fcntl(fildes, F_DUP2FD, fildes2).


Ths dup3() function works similarly to the dup2() function with two
exceptions. If fildes and fildes2 point to the same file descriptor, -1
is returned and errno set to EINVAL. If flags is O_CLOEXEC, then
filedes2 will have the FD_CLOEXEC flag set causing the file descriptor to
be closed during any future call of exec(2).

RETURN VALUES


Upon successful completion a non-negative integer representing the file
descriptor is returned. Otherwise, -1 is returned and errno is set to
indicate the error.

ERRORS


The dup2() and dup3() functions will fail if:

EBADF
The fildes argument is not a valid open file descriptor.


EBADF
The fildes2 argument is negative or is not less than the
current resource limit returned by getrlimit(RLIMIT_NOFILE,
...).


EINTR
A signal was caught during the dup2() call.


EMFILE
The process has too many open files. See fcntl(2).


Additionally, the dup3() function will fail if:

EINVAL
flags has a value other than 0 or O_CLOEXEC or fildes and
fildes2 point to the same file descriptor.


ATTRIBUTES


See attributes(5) for descriptions of the following attributes:


+--------------------+-------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-------------------+
|Interface Stability | Standard |
+--------------------+-------------------+
|MT-Level | Async-Signal-Safe |
+--------------------+-------------------+

SEE ALSO


close(2), creat(2), exec(2), fcntl(2), getrlimit(2), open(2), pipe(2),
attributes(5), standards(5)


April 19, 2013 DUP2(3C)