Thread: Write to two files using only one file descriptor

The problem I am facing is the need to write to stdout and to another file. I want the output to be displayed on the screen and into the file. This program is similar to the script command already available, but it is very simplified.

Anyway. So far I have found it simple to write to two file descriptors going to place (dup/dup2) but what I want to do is the opposite.

So, like this:
--<==
not like this:
==>--.

Make sense?

I don't have any code yet, as I am solving the problem before I start to code.

Thanks for your time!

Thanks a lot, but that didn't really solve the issue...

Basically, I am writing a simple shell. So the output from the commands entered into the shell (such as cp, rm, mv) would go to stdout and to the file. Also, stdin would be read into the program and into the file, though that would be easier.

I was hoping to do this (simplified psuedocode):

Code:

if tracing
    set stdout to output to file and stdout //the hard part
    call executeCommand(command to be executed)  //does all the exec() work
end if

That being said, however, the assignment specifications do not specifically state that I have to output everything to the terminal.

If I do not output to terminal, I think I could dup2(file, fileno(stdout)) and be done with it. What do you think of that?

Again, thanks for your time!

I just figured it out...

Code:

#include <stdio.h>
#include <fcntl.h>

int main()
{
   int file;
   int newstdout;
   file=open("filename", O_WRONLY);

   dup2(fileno(stdout), newstdout);
   perror("dup2);
   dup2(file, fileno(stdout));
   perror("dup2");
   printf("hello world\n");
   write(newstdout, "funny\n", 10);
   return 0;
}

I had to save the actual stdout somewhere else. I wont be able to get the output from commands into the actual stdout, but I can get my prompts to stdout.

Anyway, thanks!

newstdout is not initialized.