How does dup2 work in C?

The dup2() function duplicates an open file descriptor. Specifically, it provides an alternate interface to the service provided by the fcntl() function using the F_DUPFD constant command value, with fildes2 for its third argument. The duplicated file descriptor shares any locks with the original.

What is dup2 system call?

dup2() The dup2() system call performs the same task as dup(), but instead of using the lowest-numbered unused file descriptor, it uses the file descriptor number specified in newfd. In other words, the file descriptor newfd is adjusted so that it now refers to the same open file description as oldfd.

What is dup and dup2?

The difference between dup and dup2 is that dup assigns the lowest available file descriptor number, while dup2 lets you choose the file descriptor number that will be assigned and atomically closes and replaces it if it’s already taken.

What does dup2 function do?

The dup2() function returns a descriptor with the value fildes2. The descriptor refers to the same file as fildes, and it will close the file that fildes2 was associated with. If the original file descriptor was opened in text mode, data conversion is also done on the duplicated file descriptor.

How is the dup2 function used in C?

This article will explain several methods of how to use the dup2 function in C. Files are usually manipulated after they have been opened using the open system call. On success, open returns a new file descriptor associated with the newly opened file.

How is a DUP descriptor used in a file?

The dup() system call creates a copy of a file descriptor. It uses the lowest-numbered unused descriptor for the new descriptor. If the copy is successfully created, then the original and copy file descriptors may be used interchangeably. They both refer to the same open file description and thus share file offset and file status flags.

How does dup2 redirect output to a file?

Notice that this code essentially does the same thing as previously: it redirects output to a file. However, there’s a very important difference here. If the process forks-and-execs, the child process will still have its output redirected to file, even after the exec!.

What happens if DUP ( ) and dup2 ( ) fail?

Include the header file unistd.h for using dup () and dup2 () system call. If the descriptor newfd was previously open, it is silently closed before being reused. If oldfd is not a valid file descriptor, then the call fails, and newfd is not closed.