DUP2(2,L)                   AIX Technical Reference                   DUP2(2,L)



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dup2



PURPOSE

Duplicates an open file descriptor.

SYNTAX

int dup2 (oldfd, newfd)
int oldfd, newfd;

DESCRIPTION

The dup2 system call duplicates the file descriptor, oldfd, to the new file
descriptor, newfd.  When you specify a value of newfd that is already in use,
the descriptor is deallocated as if a close system call had been issued.

The oldfd parameter is a small nonnegative integer index in the descriptor
table.  Its value must be less than the size of the descriptor table obtained
by the getdtablesize subroutine.

Note:  Since newfd and oldfd are duplicate references to an open file once the
       dup2 system call has been called, the read, write, and lseek system
       calls move a single pointer into that file.  Append mode and both
       non-blocking I/O and asynchronous I/O options are then shared between
       the references.  Therefore, if you want to place a separate pointer in
       the file, you should issue an additional open system call to obtain a
       different object reference instead of using the dup2 system call.

The new file descriptor is set to remain open across exec system calls.  If the
Transparent Computing Facility is installed, the new file descriptor is also
set to remain open across rexec and run system calls.  (For more information
about file control, see "fcntl, flock, lockf.")

RETURN VALUE

When the call succeeds, a file descriptor (nonnegative integer) is returned.
If the dup2 system call fails, a value of -1 is returned, and errno is set to
indicate the error.

ERROR CONDITIONS

The dup2 system call fails if one or more of the following is true:

EBADF   The oldfd parameter is not a valid open file descriptor.

EBADF   The newfd parameter is not between 0 and 199, which is the valid range
        for file descriptors.




Processed November 7, 1990         DUP2(2,L)                                  1

DUP2(2,L)                   AIX Technical Reference                   DUP2(2,L)



RELATED INFORMATION

In this book:  "accept," "close, closex," "dup," "fcntl, flock, lockf,"
"getdtablesize," "open, openx, creat," "pipe,"  "socket," and "socketpair."



















































Processed November 7, 1990         DUP2(2,L)                                  2