What is the difference between dup and dup2?

What is the difference between 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.

Does dup close file descriptor?

The target file descriptor, when using dup() , is always an unused one. when using dup2() , is implicitly closed and replaced by a copy of the source fd.

What is dup and dup2 in C?

The dup() and dup2() functions provide an alternative interface to the service provided by fcntl() using the F_DUPFD command. The call: fid = dup(fildes); shall be equivalent to: fid = fcntl(fildes, F_DUPFD, 0);

Does dup2 close?

If you dup2(a, STDOUT_FILENO) , you close stdout and you make stdout ‘s file descriptor point to the same file table entry as a . Any program that writes to stdout will then be writing to the file instead, since stdout ‘s file descriptor is pointing to the file you dupped.

What does dup2 return?

RETURN VALUES If successful, dup2() returns a nonnegative integer; namely, the duplicated file descriptor, which is the lowest available descriptor. If failed, it returns a -1 and sets errno to the corresponding value.

What is dup2 return policy?

Does dup2 return?

What is dup2 used for?

The dup2() system function is used to create a copy of an existing file descriptor. In Linux, there are 3 standard file descriptors. They are: stdin: This is the standard input file descriptor.

What is dup dup2?

The dup() system call allocates a new file descriptor that refers to the same open file description as the descriptor oldfd. 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.

What is the difference between dup2() and close-on-exec?

The close-on-exec flag ( FD_CLOEXEC; see fcntl (2)) for the duplicate descriptor is off. 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.

What is the use of dup2 system call?

A tricky use of dup2 () system call: As in dup2 (), in place of newfd any file descriptor can be put. Below is a C implementation in which the file descriptor of Standard output (stdout) is used. This will lead all the printf () statements to be written in the file referred by the old file descriptor.

How do I make a copy of dup2?

int dup2 (int oldfd, int newfd); oldfd: old file descriptor newfd new file descriptor which is used by dup2 () to create a copy. 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.

What does DUP mean in Linux?

DESCRIPTION top The dup () system call allocates a new file descriptor that refers to the same open file description as the descriptor oldfd. (For an explanation of open file descriptions, see open (2).) The new file descriptor number is guaranteed to be the lowest-numbered file descriptor that was unused in the calling process.