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+~~Exercise.#~~
+<code c>
+#include <unistd.h>
+int main(void) {
+  sleep(5);
+  write(1, "about to fork...\n", 17);
+  fork();
+  write(1, "forked.\n", 8);
+  sleep(5);
+  return 0;
+}
+</code>
+~~Exercise.#~~
+<code c>
+#include <stdio.h>
+#include <sys/types.h>
+#include <unistd.h>
+int main(void) {
+  pid_t f = fork();
+  printf("fork: %-10dpid: %-10dppid: %-10d\n", f, getpid(), getppid());
+  return 0;
+}
+</code>
+~~Exercise.#~~
+<code c>
+#include <unistd.h>
+int main(void) {
+  if (fork()) {
+    write(1, "parent\n", 7);
+  } else {
+    write(1, "child\n", 6);
+  }
+  return 0;
+}
+</code>
+~~Exercise.#~~
+<code c>
+#include <unistd.h>
+int main(void) {
+  if (fork()) {
+    char c;
+    read(0, &c, 1);
+  }
+  return 0;
+}
+</code>
+~~Exercise.#~~
+<code c>
+#include <stdio.h>
+#include <unistd.h>
+int main(void) {
+  execlp("ps", "ps", "-F", NULL);
+  perror("execvp");
+  return -1;
+}
+</code>
+~~Exercise.#~~
+<code c>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+int main(int argc, char *argv[]) {
+  char **av = malloc(sizeof(char *) * (argc + 4));
+  char a0[] = "ls";    av[0] = a0;
+  char a1[] = "-l";    av[1] = a1;
+  char a2[] = "-t";    av[2] = a2;
+  char a3[] = "-r";    av[3] = a3;
+  for (int i = 0; i < argc; ++i)
+    av[i + 4] = argv[i + 1];
+  execvp("ls", av);
+  perror("execvp");
+  return -1;
+}
+</code>
+~~Exercise.#~~
+<code c>
+#include <stdio.h>
+#include <sys/wait.h>
+#include <time.h>
+#include <unistd.h>
+int main(int argc, char *argv[]) {
+  struct timespec start, end;
+  timespec_get(&start, TIME_UTC);
+  if (!fork()) {
+    execvp(argv[1], argv + 1);
+    perror("execvp");
+    return -1;
+  }
+  wait(NULL);
+  timespec_get(&end, TIME_UTC);
+  double elapsedSec = (end.tv_sec - start.tv_sec) + (end.tv_nsec - start.tv_nsec) / 1e9;
+  printf("%f\n", elapsedSec);
+  return 0;
+}
+</code>
+~~Exercise.#~~
+<code c>
+#include <assert.h>
+#include <stdio.h>
+#include <sys/wait.h>
+#include <time.h>
+#include <unistd.h>
+int main(int argc, char *argv[]) {
+  struct timespec start, end;
+  timespec_get(&start, TIME_UTC);
+  if (!fork()) {
+    execvp(argv[1], argv + 1);
+    perror("execvp");
+    return -1;
+  }
+  close(0);
+  close(1);
+  int status;
+  wait(&status);
+  timespec_get(&end, TIME_UTC);
+  double elapsedSec = (end.tv_sec - start.tv_sec) + (end.tv_nsec - start.tv_nsec) / 1e9;
+  if (WIFEXITED(status)) {
+    // You may test exit status by compiling & using the following program:
+    // main(int,char**v){return atoi(v[1]);}
+    fprintf(stderr, "%f (returned %d)\n", elapsedSec, WEXITSTATUS(status));
+  } else {
+    assert(WIFSIGNALED(status));
+    fprintf(stderr, "%f (killed by signal %d)\n", elapsedSec, WTERMSIG(status));
+  }
+  return 0;
+}
+</code>
+~~Exercise.#~~
+<code c>
+#include <fcntl.h>
+#include <stdio.h>
+#include <unistd.h>
+int main() {
+  int fd = open("output", O_WRONLY | O_TRUNC | O_CREAT, 0666);
+  if (fd == -1) {
+    perror("output");
+    return 1;
+  }
+  dup2(fd, 1);
+  close(fd);
+  execlp("ps", "ps", "-F", NULL);
+  return 1;
+}
+</code>
+~~Exercise.#~~
+<code c>
+#include <fcntl.h>
+#include <stdio.h>
+#include <unistd.h>
+int main(int argc, char **argv) {
+  if (argc < 2) {
+    write(2, "Too few arguments\n", 18);
+    return 1;
+  }
+  int fd = open(argv[1], O_RDONLY);
+  if (fd == -1) {
+    perror(argv[1]);
+    return 1;
+  }
+  dup2(fd, 0);
+  close(fd);
+  argv[1] = "tr";
+  execvp("tr", argv + 1);
+  return 1;
+}
+</code>
+~~Exercise.#~~
+<code c>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <unistd.h>
+int main() {
+  int fileFd = open("file", O_WRONLY | O_CREAT | O_TRUNC, 0666);
+  if (fileFd == -1) {
+    perror("file");
+    return 1;
+  }
+  int errorFd = dup(2);
+  errno = ELOOP;
+  perror("ELOOP");
+  dup2(fileFd, 2);
+  perror("ELOOP");
+  errno = EMFILE;
+  dup2(errorFd, 2);
+  perror("EMFILE");
+  dup2(fileFd, 2);
+  perror("EMFILE");
+  close(errorFd);
+  close(fileFd);
+  return 1;
+}
+</code>
+~~Exercise.#~~
+<code c>
+#include <stdint.h>
+#include <stdio.h>
+#include <unistd.h>
+int32_t doExpensiveComputation() { return 2 + 2; }
+int main() {
+  int pfds[2];
+  pipe(pfds);
+  if (!fork()) {
+    int32_t result = doExpensiveComputation();
+    write(pfds[1], &result, 4);
+    return 0;
+  }
+  int32_t result;
+  read(pfds[0], &result, 4);
+  printf("The result is: %d\n", result);
+  return 0;
+}
+</code>
+++++ The following version does a minimum of error checking. |
+<code c>
+#include <errno.h>
+#include <stdint.h>
+#include <unistd.h>
+int32_t doExpensiveComputation() { return 2 + 2; }
+int main() {
+  int pfds[2];
+  if (pipe(pfds) == -1) {
+    perror("pipe");
+    return 1;
+  }
+  int f = fork();
+  if (f == -1) {
+    perror("fork");
+    return 1;
+  }
+  if (!f) {
+    int32_t result = doExpensiveComputation();
+    write(pfds[1], &result, 4);
+    return 0;
+  }
+  int32_t result;
+  read(pfds[0], &result, 4);
+  printf("The result is: %d\n", result);
+  return 0;
+}
+</code>
+++++
+~~Exercise.#~~
+<code c>
+#include <stdint.h>
+#include <stdio.h>
+#include <sys/wait.h>
+#include <unistd.h>
+int32_t doExpensiveComputation() {
+  sleep(3);
+  return 2 + 2;
+}
+int main() {
+  int pfds[2];
+  pipe(pfds);
+  for (int i = 0; i < 3; ++i) {
+    if (!fork()) {
+      int32_t result = doExpensiveComputation();
+      write(pfds[1], &result, 4);
+      return 0;
+    }
+  }
+  int32_t result[4];
+  result[3] = doExpensiveComputation();
+  for (int i = 0; i < 3; ++i) {
+    read(pfds[0], result + i, 4);
+    wait(NULL);
+  }
+  printf("The result is: %d\n", result[0] + result[1] + result[2] + result[3]);
+  return 0;
+}
+</code>
+~~Exercise.#~~
+<code c>
+#include <ctype.h>
+#include <stdio.h>
+#include <unistd.h>
+int main() {
+  int pfds[2];
+  pipe(pfds);
+  if (!fork()) {
+    dup2(pfds[1], 1);
+    close(pfds[0]);
+    close(pfds[1]);
+    execlp("ls", "ls", "-l", NULL);
+    return 1;
+  }
+  close(pfds[1]);
+  char c;
+  while (1 == read(pfds[0], &c, 1)) {
+    c = toupper(c);
+    write(1, &c, 1);
+  }
+  return 0;
+}
+</code>
+~~Exercise.#~~
+<code c>
+#include <unistd.h>
+int main() {
+  int pfds[2];
+  pipe(pfds);
+  if (!fork()) {
+    dup2(pfds[1], 1);
+    close(pfds[0]);
+    close(pfds[1]);
+    execlp("ps", "ps", "-eF", NULL);
+    return 1;
+  }
+  dup2(pfds[0], 0);
+  close(pfds[0]);
+  close(pfds[1]);
+  execlp("sort", "sort", "-nk6", NULL);
+  return 1;
+}
+</code>
+~~META:
+language = en
+~~

Jan Kończak

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