child redirects stdout to file p4.output then runs wc
$ cat -n ostep/code/cpu-api/p4.c
1 #include <stdio.h>
2 #include <stdlib.h>
3 #include <unistd.h>
4 #include <string.h>
5 #include <fcntl.h>
6 #include <assert.h>
7 #include <sys/wait.h>
8
9 int
10 main(int argc, char *argv[])
11 {
12 int rc = fork();
13 if (rc < 0) {
14 // fork failed; exit
15 fprintf(stderr, "fork failed\n");
16 exit(1);
17 } else if (rc == 0) {
18 // child: redirect standard output to a file
19 close(STDOUT_FILENO);
20 open("./p4.output", O_CREAT|O_WRONLY|O_TRUNC, S_IRWXU);
21
22 // now exec "wc"...
23 char *myargs[3];
24 myargs[0] = strdup("wc"); // program: "wc" (word count)
25 myargs[1] = strdup("p4.c"); // argument: file to count
26 myargs[2] = NULL; // marks end of array
27 execvp(myargs[0], myargs); // runs word count
28 } else {
29 // parent goes down this path (original process)
30 int wc = wait(NULL);
31 assert(wc >= 0);
32 }
33 return 0;
34 }
$ ./p4
$ cat p4.output
34 114 884 p4.c
$
