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,
int 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).
The
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(7) 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(7),
standards(7) February 17, 2023
DUP2(3C)