freopen and execvp in c

Question

I am doing a minor shell implementation in c, and I am stuck.

I want to be able to redirect stdin and stdout, but I am confused. In, my shell, when I want to start a program, I use the execvp function. Now I would like to be able to redirect stdout, so If I run another process, the output should be redirected to a file instead of the screen.

Here is sample code:

pid_t pid;

// Child process
pid = vfork();

if((pid == 0)){
    freopen("myfile.txt", "w", stdout);
    char* arr[3];
    arr[0] = "cat";
    arr[1] = "someFileToCat.txt";
    arr[2] = NULL;
   execvp("cat", arr);
   fclose(stdout);
}

It does however print in the terminal, and not in the file.

possible duplicate of [Redirecting exec output to a buffer or file](http://stackoverflow.com/questions/2605130/redirecting-exec-output-to-a-buffer-or-file) — ChrisF, Sep 30 '12 at 20:30

score 3 · Accepted Answer · edited May 23 '17 at 12:12

3

File streams are a C abstraction. What you are looking for are lower level system calls such as open, close, and dup2.

See Redirecting exec output to a buffer or file for a full example.

edited May 23 '17 at 12:12

Community

1
1

answered Sep 30 '12 at 17:21

epsalon

2,294
12
19

freopen and execvp in c

1 Answers1