dup2 - duplicate an open file descriptor
int dup2 (int fildes, int fildes2);
fildes is a file descriptor referring to an open file, and fildes2 is a
non-negative integer less than the maximum number of open files
available. dup2 causes fildes2 to refer to the same file as fildes. If
fildes2 already referred 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.
dup2 will fail if one or more of the following are true:
EBADF fildes is not a valid open file descriptor.
EBADF fildes2 is negative or greater than or equal to the
maximum number of open files available.
EINTR a signal was caught during the dup2 call.
EMFILE The maximum number of file descriptors are currently open.
creat(2), close(2), exec(2), fcntl(2), open(2), pipe(2), lockf(3C),
Upon successful completion a non-negative integer, namely, the file
descriptor, is returned. Otherwise, a value of -1 is returned and errno
is set to indicate the error.
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