Allocate a new descriptor that refers to a file specified by a
    file descriptor returned by open, creat, or pipe.

    Format

      #include  <unistd.h>

      int dup  (int file_desc1);

      int dup2  (int file_desc1, int file_desc2);

1 - Arguments

 file_desc1

    The file descriptor being duplicated.

 file_desc2

    The new file descriptor to be assigned to the file designated by
    file_desc1.

2 - Description

    The dup function causes a previously unallocated descriptor to
    refer to its argument, while the dup2 function causes its second
    argument to refer to the same file as its first argument.

    The argument file_desc1 is invalid if it does not describe an
    open file; file_desc2 is invalid if the new file descriptor
    cannot be allocated. If file_desc2 is connected to an open file,
    that file is closed.

3 - Return Values

    n                  The new file descriptor.
    -1                 Indicates that an invalid argument was passed
                       to the function.