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

extern char **environ;

// simple example of redirecting stdout
int main(void) {

    int fd = open("file.txt", O_RDONLY);
    if (fd < 0) {
        perror("");
        return 1;
    }
    if (dup2(fd, 0) < 0){      
        perror("");
        return 1;
    }       
    // we won't use this.
    // we will read from the file.txt via fd from now on 
    close(fd);

    char *tr_argv[] = {"/usr/bin/tr","a-z", "A-Z",NULL};

    execve("/usr/bin/tr", tr_argv, environ);    
    perror("");
    return 0;
}