Can someone explain what dup() in C does?

Question

I know that dup, dup2, dup3 \"create a copy of the file descriptor oldfd\"(from man pages). However I can\'t digest it.

As I know file descriptors are just

Answer 1

dup() and dup2() system call

•The dup() system call duplicates an open file descriptor and returns the new file descriptor.

•The new file descriptor has the following properties in common with the original file descriptor: 1. refers to the same open file or pipe. 2. has the same file pointer -- that is, both file descriptors share one file pointer. 3. has the same access mode, whether read, write, or read and write.

• dup() is guaranteed to return a file descriptor with the lowest integer value available.It is because of this feature of returning the lowest unused file descriptor available that processes accomplish I/O redirection.

int dup(file_descriptor)

int dup2(file_descriptor1, file_descriptor2)