NAME

dup, dup2 - duplicate an open file descriptor

 SYNOPSIS

#include <unistd.h>

int dup(int fildes);
int dup2(int fildes, int fildes2);

 DESCRIPTION

The dup() and dup2() functions provide an alternative interface to the service provided by fcntl() using the F_DUPFD command. The call:

fid = dup(fildes);

is equivalent to:

fid = fcntl(fildes, F_DUPFD, 0);

The call:

fid = dup2(fildes, fildes2);

is equivalent to:

close(fildes2);
fid = fcntl(fildes, F_DUPFD, fildes2);

except for the following:

• If fildes2 is less than 0 or greater than or equal to {OPEN_MAX}, dup2() returns -1 with errno set to [EBADF].

• If fildes is a valid file descriptor and is equal to fildes2, dup2() returns fildes2 without closing it.

• If fildes is not a valid file descriptor, dup2() returns -1 and does not close fildes2.

• The value returned is equal to the value of fildes2 upon successful completion, or is -1 upon failure.

 RETURN VALUE

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

 ERRORS

The dup() function will fail if:

[EBADF]

The fildes argument is not a valid open file descriptor.

[EMFILE]

The number of file descriptors in use by this process would exceed {OPEN_MAX}.

The dup2() function will fail if:

[EBADF]

The fildes argument is not a valid open file descriptor or the argument fildes2 is negative or greater than or equal to {OPEN_MAX} .

[EINTR]

The dup2() function was interrupted by a signal.

 EXAMPLES

None.

 APPLICATION USAGE

None.

 FUTURE DIRECTIONS

None.

 SEE ALSO

close(), fcntl(), open(), <unistd.h>.

DERIVATION

Derived from Issue 1 of the SVID.