Start homework 5.

ostep/hw5/Makefile

@@ -0,0 +1,10 @@
+TARGETS :=	hw5_1
+
+all: $(TARGETS)
+
+clean:
+	rm -f $(TARGETS)
+
+%: %.c
+	$(CC) -o $@ $<
+

ostep/hw5/hw5.txt

@@ -0,0 +1,35 @@
+Homework for chapter 5: Interlude: Process API
+
+1. Write a program that calls fork(). Before calling fork(), have the main
+program access a variable and set its value to something. What value is the
+variable in the child process? What happens to the variable when both the child
+and the parent change the value of x?
+
+2. Write a program that opens a new file with open() and then calls fork() to
+create a new process. Can both the child and the parent access the file
+descriptor returned by open()? What happens when they are writing to the file
+concurrently?
+
+3. Write another program using fork(). The child process should print "hello",
+the parent process should print "goodbye". You should try to ensure that the
+child process always prints first; can you do this without calling wait() in
+the parent?
+
+4. Write a program that calls fork() and then calls some form of exec() to run
+/bin/ls. See if you can try all the variants of exec(), including execl(),
+execle(), execlp(), execv(), execvp(), and execevP(). Why do you think there
+are so many variants of the same basic call?
+
+5. Now write a program that uses wait() to wait for the child process to finish
+in the parent. What does wait() return? What happens if you use wait() in the
+child()?
+
+6. Write a slight modification of the previous program, this time using
+waitpid() instead of wait(). When would waitpid() be useful?
+
+7. Write a program that creates a child process, and then in the child close
+standard output. What happens if the child calls printf() to print some output
+after closing the descriptor?
+
+8. Write a program that creates two children, and connects the standard output
+of one to the standard input of the other using the pipe() system call.

ostep/hw5/hw5_1.c

@@ -0,0 +1,28 @@
+#include <stdio.h>
+#include <unistd.h>
+
+
+int
+main(void)
+{
+	int	x = 10;
+	pid_t	pid;
+
+	pid = fork();
+	if (pid < 0) {
+
+	}
+	else if (pid > 0) {
+		for (int i = 0; i < 5; i++) {
+			printf("child: x=%d\n", x);
+			x++;
+			sleep(1);
+		}
+	} else {
+		for (int i = 0; i < 5; i++) {
+			printf("parent: x=%d\n", x);
+			x--;
+			sleep(1);
+		}
+	}
+}