redir.c

/* exercise on UNIX file system */
 /* useful characters: [] # */

 # include <stdio.h>
 # include <string.h>
 # include <fcntl.h> // for bitflags
 # include <stdlib.h> // for exit()

 # define errormsg(x) { puts(x); exit(1); }

 int main(int argc, char * argv[])
    {
     // checking proper input format
     if(argc != 2) errormsg("Error: Invalid input length");

     // opening (and then closing) file
     int file = open(*(argv + 1), O_CREAT|O_TRUNC|O_WRONLY);
     if(file == -1) errormsg("Error: Incorrect file name");
     close(1); // closes stdout, why?
     dup(file); // why duplicate?

     // fork
     int pid, status;
     pid = fork();
     if(pid != 0)
    wait(&status); // waits for the child process
     execve("./writer", NULL, NULL); // calls the writer function
     errormsg("Error: execve() call failed");
    }