Detect and exit on write errors.

usr.bin/yes/yes.c

@@ -51,8 +51,11 @@ int
 main(int argc, char **argv)
 {
 	if (argc > 1)
-		for(;;)
-			puts(argv[1]);
-	else for (;;)
-		puts("y");
+		while (puts(argv[1]) != EOF)
+			;
+	else
+		while (puts("y") != EOF)
+			;
+	err(1, "stdout");
+	/*NOTREACHED*/
 }