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 numbers to keep track of file locations and their direction(input/output). Wouldn't it be easier to just
fd=fd2;
Whenever we want to duplicate a file descriptor?
And something else..
dup() uses the lowest-numbered unused descriptor for the new descriptor.
Does that mean that it can also take as value stdin, stdout or stderr if we assume that we have close()-ed one of those?
Just wanted to respond to myself on the second question after experimenting a bit.
The answer is YES. A file descriptor that you make can take a value 0, 1, 2 if stdin, stdout or stderr are closed.
Example:
close(1); //closing stdout
newfd=dup(1); //newfd takes value of least available fd number
Where this happens to file descriptors:
0 stdin .--------------. 0 stdin .--------------. 0 stdin
1 stdout =| close(1) :=> 2 stderr =| newfd=dup(1) :=> 1 newfd
2 stderr '--------------' '--------------' 2 stderr