diff --git a/Makefile b/Makefile
index 980e035..eaa1f8c 100644
--- a/Makefile
+++ b/Makefile
@@ -14,6 +14,7 @@ SRC_DIR        	:= .
 OBJ_DIR 		:= obj
 SPROJS_INCLUDE 	:= -I.  
 
+HOSTFS_ROOT := hostfs_root
 ifneq (,)
   march := -march=
   is_32bit := $(findstring 32,$(march))
@@ -63,12 +64,41 @@ SPIKE_INF_LIB   := $(OBJ_DIR)/spike_interface.a
 
 
 #---------------------	user   -----------------------
-USER_CPPS 		:= user/*.c 
+USER_CPPS 		:= user/app_shell.c user/user_lib.c
 
-USER_CPPS  		:= $(wildcard $(USER_CPPS))
 USER_OBJS  		:= $(addprefix $(OBJ_DIR)/, $(patsubst %.c,%.o,$(USER_CPPS)))
 
-USER_TARGET 	:= $(OBJ_DIR)/app_hardlink
+USER_TARGET 	:= $(HOSTFS_ROOT)/bin/app_shell
+
+USER_E_CPPS 		:= user/app_ls.c user/user_lib.c
+
+USER_E_OBJS  		:= $(addprefix $(OBJ_DIR)/, $(patsubst %.c,%.o,$(USER_E_CPPS)))
+
+USER_E_TARGET 	:= $(HOSTFS_ROOT)/bin/app_ls
+
+USER_M_CPPS 		:= user/app_mkdir.c user/user_lib.c
+
+USER_M_OBJS  		:= $(addprefix $(OBJ_DIR)/, $(patsubst %.c,%.o,$(USER_M_CPPS)))
+
+USER_M_TARGET 	:= $(HOSTFS_ROOT)/bin/app_mkdir
+
+USER_T_CPPS 		:= user/app_touch.c user/user_lib.c
+
+USER_T_OBJS  		:= $(addprefix $(OBJ_DIR)/, $(patsubst %.c,%.o,$(USER_T_CPPS)))
+
+USER_T_TARGET 	:= $(HOSTFS_ROOT)/bin/app_touch
+
+USER_C_CPPS 		:= user/app_cat.c user/user_lib.c
+
+USER_C_OBJS  		:= $(addprefix $(OBJ_DIR)/, $(patsubst %.c,%.o,$(USER_C_CPPS)))
+
+USER_C_TARGET 	:= $(HOSTFS_ROOT)/bin/app_cat
+
+USER_O_CPPS 		:= user/app_echo.c user/user_lib.c
+
+USER_O_OBJS  		:= $(addprefix $(OBJ_DIR)/, $(patsubst %.c,%.o,$(USER_O_CPPS)))
+
+USER_O_TARGET 	:= $(HOSTFS_ROOT)/bin/app_echo
 #------------------------targets------------------------
 $(OBJ_DIR):
 	@-mkdir -p $(OBJ_DIR)	
@@ -76,7 +106,12 @@ $(OBJ_DIR):
 	@-mkdir -p $(dir $(SPIKE_INF_OBJS))
 	@-mkdir -p $(dir $(KERNEL_OBJS))
 	@-mkdir -p $(dir $(USER_OBJS))
-
+	@-mkdir -p $(dir $(USER_E_OBJS))
+	@-mkdir -p $(dir $(USER_M_OBJS))
+	@-mkdir -p $(dir $(USER_T_OBJS))
+	@-mkdir -p $(dir $(USER_C_OBJS))
+	@-mkdir -p $(dir $(USER_O_OBJS))
+	
 $(OBJ_DIR)/%.o : %.c
 	@echo "compiling" $<
 	@$(COMPILE) -c $< -o $@
@@ -102,20 +137,52 @@ $(KERNEL_TARGET): $(OBJ_DIR) $(UTIL_LIB) $(SPIKE_INF_LIB) $(KERNEL_OBJS) $(KERNE
 
 $(USER_TARGET): $(OBJ_DIR) $(UTIL_LIB) $(USER_OBJS)
 	@echo "linking" $@	...	
+	-@mkdir -p $(HOSTFS_ROOT)/bin
 	@$(COMPILE) --entry=main $(USER_OBJS) $(UTIL_LIB) -o $@
 	@echo "User app has been built into" \"$@\"
+	@cp $@ $(OBJ_DIR)
+
+$(USER_E_TARGET): $(OBJ_DIR) $(UTIL_LIB) $(USER_E_OBJS)
+	@echo "linking" $@	...	
+	-@mkdir -p $(HOSTFS_ROOT)/bin
+	@$(COMPILE) --entry=main $(USER_E_OBJS) $(UTIL_LIB) -o $@
+	@echo "User app has been built into" \"$@\"
+
+$(USER_M_TARGET): $(OBJ_DIR) $(UTIL_LIB) $(USER_M_OBJS)
+	@echo "linking" $@	...	
+	-@mkdir -p $(HOSTFS_ROOT)/bin
+	@$(COMPILE) --entry=main $(USER_M_OBJS) $(UTIL_LIB) -o $@
+	@echo "User app has been built into" \"$@\"
+
+$(USER_T_TARGET): $(OBJ_DIR) $(UTIL_LIB) $(USER_T_OBJS)
+	@echo "linking" $@	...	
+	-@mkdir -p $(HOSTFS_ROOT)/bin
+	@$(COMPILE) --entry=main $(USER_T_OBJS) $(UTIL_LIB) -o $@
+	@echo "User app has been built into" \"$@\"
+
+$(USER_C_TARGET): $(OBJ_DIR) $(UTIL_LIB) $(USER_C_OBJS)
+	@echo "linking" $@	...	
+	-@mkdir -p $(HOSTFS_ROOT)/bin
+	@$(COMPILE) --entry=main $(USER_C_OBJS) $(UTIL_LIB) -o $@
+	@echo "User app has been built into" \"$@\"
+
+$(USER_O_TARGET): $(OBJ_DIR) $(UTIL_LIB) $(USER_O_OBJS)
+	@echo "linking" $@	...	
+	-@mkdir -p $(HOSTFS_ROOT)/bin
+	@$(COMPILE) --entry=main $(USER_O_OBJS) $(UTIL_LIB) -o $@
+	@echo "User app has been built into" \"$@\"
 
 -include $(wildcard $(OBJ_DIR)/*/*.d)
 -include $(wildcard $(OBJ_DIR)/*/*/*.d)
 
 .DEFAULT_GOAL := $(all)
 
-all: $(KERNEL_TARGET) $(USER_TARGET)
+all: $(KERNEL_TARGET) $(USER_TARGET) $(USER_E_TARGET) $(USER_M_TARGET) $(USER_T_TARGET) $(USER_C_TARGET) $(USER_O_TARGET)
 .PHONY:all
 
-run: $(KERNEL_TARGET) $(USER_TARGET)
+run: $(KERNEL_TARGET) $(USER_TARGET) $(USER_E_TARGET) $(USER_M_TARGET) $(USER_T_TARGET) $(USER_C_TARGET) $(USER_O_TARGET)
 	@echo "********************HUST PKE********************"
-	spike $(KERNEL_TARGET) $(USER_TARGET)
+	spike $(KERNEL_TARGET) /bin/app_shell
 
 # need openocd!
 gdb:$(KERNEL_TARGET) $(USER_TARGET)
@@ -146,4 +213,4 @@ format:
 	@python ./format.py ./
 
 clean:
-	rm -fr ${OBJ_DIR}
+	rm -fr ${OBJ_DIR} ${HOSTFS_ROOT}/bin
diff --git a/hostfs_root/hostfile.txt b/hostfs_root/hostfile.txt
deleted file mode 100644
index cfbea73..0000000
--- a/hostfs_root/hostfile.txt
+++ /dev/null
@@ -1,2 +0,0 @@
-This is an apple. 
-Apples are good for our health. 
diff --git a/hostfs_root/shellrc b/hostfs_root/shellrc
new file mode 100644
index 0000000..26ce3b9
--- /dev/null
+++ b/hostfs_root/shellrc
@@ -0,0 +1,8 @@
+/bin/app_mkdir /RAMDISK0/sub_dir
+/bin/app_touch /RAMDISK0/sub_dir/ramfile1
+/bin/app_touch /RAMDISK0/sub_dir/ramfile2
+/bin/app_echo /RAMDISK0/sub_dir/ramfile1
+/bin/app_cat /RAMDISK0/sub_dir/ramfile1
+/bin/app_ls /RAMDISK0/sub_dir
+/bin/app_ls /RAMDISK0
+END END
diff --git a/kernel/elf.c b/kernel/elf.c
index 5010a01..b354510 100644
--- a/kernel/elf.c
+++ b/kernel/elf.c
@@ -8,10 +8,11 @@
 #include "riscv.h"
 #include "vmm.h"
 #include "pmm.h"
+#include "vfs.h"
 #include "spike_interface/spike_utils.h"
 
 typedef struct elf_info_t {
-  spike_file_t *f;
+  struct file *f;
   process *p;
 } elf_info;
 
@@ -34,14 +35,12 @@ static void *elf_alloc_mb(elf_ctx *ctx, uint64 elf_pa, uint64 elf_va, uint64 siz
 }
 
 //
-// actual file reading, using the spike file interface.
+// actual file reading, using the vfs file interface.
 //
 static uint64 elf_fpread(elf_ctx *ctx, void *dest, uint64 nb, uint64 offset) {
   elf_info *msg = (elf_info *)ctx->info;
-  // call spike file utility to load the content of elf file into memory.
-  // spike_file_pread will read the elf file (msg->f) from offset to memory (indicated by
-  // *dest) for nb bytes.
-  return spike_file_pread(msg->f, dest, nb, offset);
+  vfs_lseek(msg->f, offset, SEEK_SET);
+  return vfs_read(msg->f, dest, nb);
 }
 
 //
@@ -107,50 +106,18 @@ elf_status elf_load(elf_ctx *ctx) {
   return EL_OK;
 }
 
-typedef union {
-  uint64 buf[MAX_CMDLINE_ARGS];
-  char *argv[MAX_CMDLINE_ARGS];
-} arg_buf;
-
-//
-// returns the number (should be 1) of string(s) after PKE kernel in command line.
-// and store the string(s) in arg_bug_msg.
-//
-static size_t parse_args(arg_buf *arg_bug_msg) {
-  // HTIFSYS_getmainvars frontend call reads command arguments to (input) *arg_bug_msg
-  long r = frontend_syscall(HTIFSYS_getmainvars, (uint64)arg_bug_msg,
-      sizeof(*arg_bug_msg), 0, 0, 0, 0, 0);
-  kassert(r == 0);
-
-  size_t pk_argc = arg_bug_msg->buf[0];
-  uint64 *pk_argv = &arg_bug_msg->buf[1];
-
-  int arg = 1;  // skip the PKE OS kernel string, leave behind only the application name
-  for (size_t i = 0; arg + i < pk_argc; i++)
-    arg_bug_msg->argv[i] = (char *)(uintptr_t)pk_argv[arg + i];
-
-  //returns the number of strings after PKE kernel in command line
-  return pk_argc - arg;
-}
-
 //
 // load the elf of user application, by using the spike file interface.
 //
-void load_bincode_from_host_elf(process *p) {
-  arg_buf arg_bug_msg;
-
-  // retrieve command line arguements
-  size_t argc = parse_args(&arg_bug_msg);
-  if (!argc) panic("You need to specify the application program!\n");
-
-  sprint("Application: %s\n", arg_bug_msg.argv[0]);
+void load_bincode_from_host_elf(process *p, char *filename) {
+  sprint("Application: %s\n", filename);
 
   //elf loading. elf_ctx is defined in kernel/elf.h, used to track the loading process.
   elf_ctx elfloader;
   // elf_info is defined above, used to tie the elf file and its corresponding process.
   elf_info info;
 
-  info.f = spike_file_open(arg_bug_msg.argv[0], O_RDONLY, 0);
+  info.f = vfs_open(filename, O_RDONLY);
   info.p = p;
   // IS_ERR_VALUE is a macro defined in spike_interface/spike_htif.h
   if (IS_ERR_VALUE(info.f)) panic("Fail on openning the input application program.\n");
@@ -165,8 +132,8 @@ void load_bincode_from_host_elf(process *p) {
   // entry (virtual, also physical in lab1_x) address
   p->trapframe->epc = elfloader.ehdr.entry;
 
-  // close the host spike file
-  spike_file_close( info.f );
+  // close the vfs file
+  vfs_close( info.f );
 
   sprint("Application program entry point (virtual address): 0x%lx\n", p->trapframe->epc);
 }
diff --git a/kernel/elf.h b/kernel/elf.h
index 3011dc5..7d06f19 100644
--- a/kernel/elf.h
+++ b/kernel/elf.h
@@ -63,6 +63,6 @@ typedef struct elf_ctx_t {
 elf_status elf_init(elf_ctx *ctx, void *info);
 elf_status elf_load(elf_ctx *ctx);
 
-void load_bincode_from_host_elf(process *p);
+void load_bincode_from_host_elf(process *p, char *filename);
 
 #endif
diff --git a/kernel/kernel.c b/kernel/kernel.c
index b30b793..5cf0301 100644
--- a/kernel/kernel.c
+++ b/kernel/kernel.c
@@ -33,6 +33,32 @@ void enable_paging() {
   flush_tlb();
 }
 
+typedef union {
+  uint64 buf[MAX_CMDLINE_ARGS];
+  char *argv[MAX_CMDLINE_ARGS];
+} arg_buf;
+
+//
+// returns the number (should be 1) of string(s) after PKE kernel in command line.
+// and store the string(s) in arg_bug_msg.
+//
+static size_t parse_args(arg_buf *arg_bug_msg) {
+  // HTIFSYS_getmainvars frontend call reads command arguments to (input) *arg_bug_msg
+  long r = frontend_syscall(HTIFSYS_getmainvars, (uint64)arg_bug_msg,
+      sizeof(*arg_bug_msg), 0, 0, 0, 0, 0);
+  kassert(r == 0);
+
+  size_t pk_argc = arg_bug_msg->buf[0];
+  uint64 *pk_argv = &arg_bug_msg->buf[1];
+
+  int arg = 1;  // skip the PKE OS kernel string, leave behind only the application name
+  for (size_t i = 0; arg + i < pk_argc; i++)
+    arg_bug_msg->argv[i] = (char *)(uintptr_t)pk_argv[arg + i];
+
+  //returns the number of strings after PKE kernel in command line
+  return pk_argc - arg;
+}
+
 //
 // load the elf, and construct a "process" (with only a trapframe).
 // load_bincode_from_host_elf is defined in elf.c
@@ -43,7 +69,13 @@ process* load_user_program() {
   proc = alloc_process();
   sprint("User application is loading.\n");
 
-  load_bincode_from_host_elf(proc);
+  arg_buf arg_bug_msg;
+
+  // retrieve command line arguements
+  size_t argc = parse_args(&arg_bug_msg);
+  if (!argc) panic("You need to specify the application program!\n");
+
+  load_bincode_from_host_elf(proc, arg_bug_msg.argv[0]);
   return proc;
 }
 
diff --git a/user/app_cat.c b/user/app_cat.c
new file mode 100644
index 0000000..6ffc1b6
--- /dev/null
+++ b/user/app_cat.c
@@ -0,0 +1,23 @@
+#include "user_lib.h"
+#include "util/string.h"
+#include "util/types.h"
+
+int main(int argc, char *argv[]) {
+  int fd;
+  int MAXBUF = 512;
+  char buf[MAXBUF];
+  char *filename = argv[0];
+
+  printu("\n======== cat command ========\n");
+  printu("cat: %s\n", filename);
+
+  fd = open(filename, O_RDWR);
+  printu("file descriptor fd: %d\n", fd);
+
+  read_u(fd, buf, MAXBUF);
+  printu("read content: \n%s\n", buf);
+  close(fd);
+
+  exit(0);
+  return 0;
+}
diff --git a/user/app_echo.c b/user/app_echo.c
new file mode 100644
index 0000000..f106728
--- /dev/null
+++ b/user/app_echo.c
@@ -0,0 +1,20 @@
+#include "user_lib.h"
+#include "util/string.h"
+#include "util/types.h"
+
+int main(int argc, char *argv[]) {
+  int fd;
+  char str[] = "hello world";
+  char *filename = argv[0];
+  printu("\n======== echo command ========\n");
+  printu("echo: %s\n", filename);
+
+  fd = open(filename, O_RDWR | O_CREAT);
+  printu("file descriptor fd: %d\n", fd);
+
+  write_u(fd, str, strlen(str));
+  printu("write content: \n%s\n", str);
+  close(fd);
+  exit(0);
+  return 0;
+}
diff --git a/user/app_hardlink.c b/user/app_hardlink.c
deleted file mode 100644
index 7e209e5..0000000
--- a/user/app_hardlink.c
+++ /dev/null
@@ -1,94 +0,0 @@
-#include "user_lib.h"
-#include "util/string.h"
-#include "util/types.h"
-
-void ls(char *path) {
-  int dir_fd = opendir_u(path);
-  printu("------------------------------\n");
-  printu("ls \"%s\":\n", path);
-  printu("[name]               [inode_num]\n");
-  struct dir dir;
-  int width = 20;
-  while(readdir_u(dir_fd, &dir) == 0) {
-    // we do not have %ms :(
-    char name[width + 1];
-    memset(name, ' ', width + 1);
-    name[width] = '\0';
-    if (strlen(dir.name) < width) {
-      strcpy(name, dir.name);
-      name[strlen(dir.name)] = ' ';
-      printu("%s %d\n", name, dir.inum);
-    }
-    else
-      printu("%s %d\n", dir.name, dir.inum);
-  }
-  printu("------------------------------\n");
-  closedir_u(dir_fd);
-}
-
-int main(int argc, char *argv[]) {
-  int MAXBUF = 512;
-  char str[] = "hello world";
-  char buf[MAXBUF];
-  int fd1, fd2;
-  
-  printu("\n======== establish the file ========\n");
-
-  fd1 = open("/RAMDISK0/ramfile", O_RDWR | O_CREAT);
-  printu("create file: /RAMDISK0/ramfile\n");
-  close(fd1);
-
-  printu("\n======== Test 1: hard link ========\n");
-
-  link_u("/RAMDISK0/ramfile", "/RAMDISK0/ramfile2");
-  printu("create hard link: /RAMDISK0/ramfile2 -> /RAMDISK0/ramfile\n");
-
-  fd1 = open("/RAMDISK0/ramfile", O_RDWR);
-  fd2 = open("/RAMDISK0/ramfile2", O_RDWR);
-  
-  printu("file descriptor fd1 (ramfile): %d\n", fd1);
-  printu("file descriptor fd2 (ramfile2): %d\n", fd2);
-
-  // check the number of hard links to ramfile on disk
-  struct istat st;
-  disk_stat_u(fd1, &st);
-  printu("ramfile hard links: %d\n", st.st_nlinks);
-  if (st.st_nlinks != 2) {
-    printu("ERROR: the number of hard links to ramfile should be 2, but it is %d\n",
-             st.st_nlinks);
-    exit(-1);
-  }
-  
-  write_u(fd1, str, strlen(str));
-  printu("/RAMDISK0/ramfile write content: \n%s\n", str);
-
-  read_u(fd2, buf, MAXBUF);
-  printu("/RAMDISK0/ramfile2 read content: \n%s\n", buf);
-
-  close(fd1);
-  close(fd2);
-
-  printu("\n======== Test 2: unlink ========\n");
-
-  ls("/RAMDISK0");
-
-  unlink_u("/RAMDISK0/ramfile");
-  printu("unlink: /RAMDISK0/ramfile\n");
-
-  ls("/RAMDISK0");
-
-  // check the number of hard links to ramfile2 on disk
-  fd2 = open("/RAMDISK0/ramfile2", O_RDWR);
-  disk_stat_u(fd2, &st);
-  printu("ramfile2 hard links: %d\n", st.st_nlinks);
-  if (st.st_nlinks != 1) {
-    printu("ERROR: the number of hard links to ramfile should be 1, but it is %d\n",
-             st.st_nlinks);
-    exit(-1);
-  }
-  close(fd2);
-
-  printu("\nAll tests passed!\n\n");
-  exit(0);
-  return 0;
-}
diff --git a/user/app_ls.c b/user/app_ls.c
new file mode 100644
index 0000000..f560038
--- /dev/null
+++ b/user/app_ls.c
@@ -0,0 +1,31 @@
+#include "user_lib.h"
+#include "util/string.h"
+#include "util/types.h"
+
+int main(int argc, char *argv[]) {
+  char *path = argv[0];
+  int dir_fd = opendir_u(path);
+  printu("---------- ls command -----------\n");
+  printu("ls \"%s\":\n", path);
+  printu("[name]               [inode_num]\n");
+  struct dir dir;
+  int width = 20;
+  while(readdir_u(dir_fd, &dir) == 0) {
+    // we do not have %ms :(
+    char name[width + 1];
+    memset(name, ' ', width + 1);
+    name[width] = '\0';
+    if (strlen(dir.name) < width) {
+      strcpy(name, dir.name);
+      name[strlen(dir.name)] = ' ';
+      printu("%s %d\n", name, dir.inum);
+    }
+    else
+      printu("%s %d\n", dir.name, dir.inum);
+  }
+  printu("------------------------------\n");
+  closedir_u(dir_fd);
+
+  exit(0);
+  return 0;
+}
\ No newline at end of file
diff --git a/user/app_mkdir.c b/user/app_mkdir.c
new file mode 100644
index 0000000..8428f8d
--- /dev/null
+++ b/user/app_mkdir.c
@@ -0,0 +1,15 @@
+#include "user_lib.h"
+#include "util/string.h"
+#include "util/types.h"
+
+
+int main(int argc, char *argv[]) {
+  char *new_dir = argv[0];
+  printu("\n======== mkdir command ========\n");
+
+  mkdir_u(new_dir);
+  printu("mkdir: %s\n", new_dir);
+
+  exit(0);
+  return 0;
+}
diff --git a/user/app_shell.c b/user/app_shell.c
new file mode 100644
index 0000000..df83692
--- /dev/null
+++ b/user/app_shell.c
@@ -0,0 +1,53 @@
+/*
+ * This app starts a very simple shell and executes some simple commands.
+ * The commands are stored in the hostfs_root/shellrc
+ * The shell loads the file and executes the command line by line.                 
+ */
+#include "user_lib.h"
+#include "string.h"
+#include "util/types.h"
+
+int main(int argc, char *argv[]) {
+  printu("\n======== Shell Start ========\n\n");
+  int fd;
+  int MAXBUF = 1024;
+  char buf[MAXBUF];
+  char *token;
+  char delim[3] = " \n";
+  fd = open("/shellrc", O_RDONLY);
+
+  read_u(fd, buf, MAXBUF);
+  close(fd);
+  char *command = naive_malloc();
+  char *para = naive_malloc();
+  int start = 0;
+  while (1)
+  {
+    if(!start) {
+      token = strtok(buf, delim);
+      start = 1;
+    }
+    else 
+      token = strtok(NULL, delim);
+    strcpy(command, token);
+    token = strtok(NULL, delim);
+    strcpy(para, token);
+    if(strcmp(command, "END") == 0 && strcmp(para, "END") == 0)
+      break;
+    printu("Next command: %s %s\n\n", command, para);
+    printu("==========Command Start============\n\n");
+    int pid = fork();
+    if(pid == 0) {
+      int ret = exec(command, para);
+      if (ret == -1)
+      printu("exec failed!\n");
+    }
+    else
+    {
+      wait(pid);
+      printu("==========Command End============\n\n");
+    }
+  }
+  exit(0);
+  return 0;
+}
diff --git a/user/app_touch.c b/user/app_touch.c
new file mode 100644
index 0000000..f79d3ba
--- /dev/null
+++ b/user/app_touch.c
@@ -0,0 +1,17 @@
+#include "user_lib.h"
+#include "util/string.h"
+#include "util/types.h"
+
+int main(int argc, char *argv[]) {
+  int fd;
+  char *filename = argv[0];
+  printu("\n======== touch command ========\n");
+  printu("touch: %s\n", filename);
+
+  fd = open(filename, O_CREAT);
+  printu("file descriptor fd: %d\n", fd);
+
+  close(fd);
+  exit(0);
+  return 0;
+}