dup – duplicate an open file descriptor|
int dup(int oldfd, int newfd)
Given a file descriptor, oldfd, referring to an open file, dup
returns a new file descriptor referring to the same file. |
If newfd is –1 the system chooses the lowest available file descriptor.
Otherwise, dup will use newfd for the new file descriptor (closing
any old file associated with newfd). File descriptors are allocated
dynamically, so to prevent unwarranted growth of the file descriptor
table, dup requires that newfd be no greater than
20 more than the highest file descriptor ever used by the program.