diff --git a/yeeshell.c b/yeeshell.c
index 5674214..eb46177 100644
--- a/yeeshell.c
+++ b/yeeshell.c
@@ -1,707 +1,713 @@
-#include <stdio.h>
-#include <stdlib.h>
-#include <unistd.h>
-#include <string.h>
-#include <dirent.h>
-#include <signal.h>
-#include <errno.h>
-#include <fcntl.h>
-#include <termcap.h>
-#include <termios.h>
-#include <curses.h>
-#include <limits.h>
-#include <pwd.h>
-#include <assert.h>
-
-#include <sys/types.h>
-#include <sys/wait.h>
-#include <sys/stat.h>
-#include <sys/times.h>
-#include <sys/time.h>
-#include <sys/select.h>
-
-#include <minix/com.h>
-#include <minix/config.h>
-#include <minix/type.h>
-#include <minix/endpoint.h>
-#include <minix/const.h>
-#include <minix/u64.h>
-#include <minix/procfs.h>
-#include <paths.h>
-
-#include "yeeshell.h"
-
-/* record cmdline history */
-char *history[CMDLINE_HISTORY_MAX_QUANTITY];
-int cmdline_amount = 0;
-
-struct proc *proc = NULL, *prev_proc = NULL;
-int order = ORDER_CPU;
-int blockedverbose = 0;
-int nr_total = 0;
-int slot = 1;
-unsigned int nr_procs, nr_tasks;
-
-int main()
-{
-	char *cmdline = NULL, *pwd = NULL;
-	char *args[ARGS_MAX_QUANTITY];
-	int status = 1;
-	pwd = (char *)calloc(PATH_MAX_SIZE, sizeof(char));
-	for (int i = 0; i < CMDLINE_HISTORY_MAX_QUANTITY; i++)
-	{
-		history[i] = (char *)calloc(CMDLINE_MAX_SIZE, sizeof(char));
-	}
-
-	/* execute the shell's read, parse and execution loop */
-	do
-	{
-		if (!getcwd(pwd, PATH_MAX_SIZE))
-		{
-			printf("yeeshell: The current path cannot be obtained!\n");
-			exit(0);
-		}
-		printf("[root@yeeshell %s]# ", pwd);
-		cmdline = readline();
-		strcpy(history[cmdline_amount++], cmdline);
-		status = execute(cmdline, args);
-		free(cmdline);
-	} while (status);
-	for (int i = 0; i < CMDLINE_HISTORY_MAX_QUANTITY; i++)
-	{
-		free(history[i]);
-	}
-	exit(EXIT_SUCCESS);
-}
-
-char *readline()
-{
-	char *cmdline = NULL;
-	ssize_t bufsize = 0;
-	getline(&cmdline, &bufsize, stdin);
-	return cmdline;
-}
-
-int parseline(char *cmdline, char **args)
-{
-	static char array[CMDLINE_MAX_SIZE]; /* holds local copy of command line */
-	char *buf = array;					 /* ptr that traverses command line */
-	char *delim;						 /* points to first space delimiter */
-	int argc;							 /* number of args */
-	int bg;								 /* background job? */
-
-	strcpy(buf, cmdline);
-	buf[strlen(buf) - 1] = ' ';	  /* replace trailing '\n' with space */
-	while (*buf && (*buf == ' ')) /* ignore leading spaces */
-	{
-		buf++;
-	}
-
-	/* Build the argv list */
-	argc = 0;
-	if (*buf == '\'')
-	{
-		buf++;
-		delim = strchr(buf, '\'');
-	}
-	else
-	{
-		delim = strchr(buf, ' ');
-	}
-
-	while (delim)
-	{
-		args[argc++] = buf;
-		*delim = '\0';
-		buf = delim + 1;
-		while (*buf && (*buf == ' ')) /* ignore spaces */
-		{
-			buf++;
-		}
-
-		if (*buf == '\'')
-		{
-			buf++;
-			delim = strchr(buf, '\'');
-		}
-		else
-		{
-			delim = strchr(buf, ' ');
-		}
-	}
-	args[argc] = NULL;
-
-	if (argc == 0) /* ignore blank line */
-	{
-		return 1;
-	}
-
-	/* should the job run in the background? */
-	if ((bg = (*args[argc - 1] == '&')) != 0)
-	{
-		args[--argc] = NULL;
-	}
-	return bg;
-}
-
-int check_redirect(char **args, char *redirect_filename, char **redirect_args)
-{
-	int i = 0, j = 0, redirect_flag = REDIRECT_NO;
-	while (args[i] != NULL)
-	{
-		if (!strcmp(args[i], ">"))
-		{
-			redirect_flag = REDIRECT_OUT;
-			break;
-		}
-		else if (!strcmp(args[i], "<"))
-		{
-			redirect_flag = REDIRECT_IN;
-			break;
-		}
-		i++;
-	}
-
-	if ((redirect_flag == 1) || (redirect_flag == 2))
-	{
-		strcpy(redirect_filename, args[i + 1]);
-		for (j = 0; j < i; j++)
-		{
-			redirect_args[j] = args[j];
-		}
-	}
-
-	return redirect_flag;
-}
-
-int do_redirect(int redirect_flag, char *redirect_filename, char **redirect_args)
-{
-	pid_t pid;
-	int fd = 1;
-	if ((pid = fork()) == 0) /* Child process */
-	{
-		if (redirect_flag == 1) /* in or out? */
-		{
-			fd = open(redirect_filename, O_CREAT | O_WRONLY | O_TRUNC, S_IRUSR | S_IWUSR | S_IXUSR);
-			close(1);
-			dup(fd);
-		}
-		else if (redirect_flag == 2)
-		{
-			fd = open(redirect_filename, O_RDONLY, S_IRUSR);
-			close(0);
-			dup(fd);
-		}
-		if (execvp(redirect_args[0], redirect_args) <= 0)
-		{
-			printf("%s: Command not found\n", redirect_args[0]);
-			exit(0);
-		}
-		close(fd);
-	}
-	else /* parent process */
-	{
-		waitpid(pid, NULL, 0);
-	}
-	return 1;
-}
-
-int check_pipe(char **args, char **pipe_arg_1, char **pipe_arg_2)
-{
-	int pipe_flag = 0, i = 0, j = 0;
-
-	while (args[i] != NULL)
-	{
-		if (!strcmp(args[i], "|"))
-		{
-			pipe_flag = 1;
-			break;
-		}
-		pipe_arg_1[j++] = args[i++];
-	}
-	pipe_arg_1[j] = NULL;
-
-	j = 0;
-	i++;
-	while (args[i] != NULL)
-	{
-		pipe_arg_2[j++] = args[i++];
-	}
-	pipe_arg_2[j] = NULL;
-	return pipe_flag;
-}
-
-int do_pipe(char **pipe_arg_1, char **pipe_arg_2)
-{
-	int fds[2];
-	pipe(fds);
-	pid_t prog_1, prog_2;
-
-	if ((prog_1 = fork()) == 0) /* Child process 1 */
-	{
-		close(1);
-		dup(fds[1]);
-		close(fds[0]);
-		close(fds[1]);
-
-		if (execvp(pipe_arg_1[0], pipe_arg_1) <= 0)
-		{
-			printf("%s: Command not found\n", pipe_arg_1[0]);
-			exit(0);
-		}
-	}
-
-	if ((prog_2 = fork()) == 0) /* Child process 2 */
-	{
-		close(0);
-		dup2(fds[0]);
-		close(fds[0]);
-		close(fds[1]);
-
-		if (execvp(pipe_arg_2[0], pipe_arg_2) <= 0)
-		{
-			printf("%s: Command not found\n", pipe_arg_2[0]);
-			exit(0);
-		}
-	}
-
-	close(fds[0]);
-	close(fds[1]);
-
-	waitpid(prog_1, NULL, 0);
-	waitpid(prog_2, NULL, 0);
-	return 1;
-}
-
-int do_bg_fg(char **args, int bg)
-{
-	pid_t pid;
-	if ((pid = fork()) == 0)
-	{
-		if (execvp(args[0], args) <= 0)
-		{
-			printf("%s: Command not found\n", args[0]);
-			exit(0);
-		}
-	}
-	else
-	{
-		if (bg)
-		{
-			signal(SIGCHLD, SIG_IGN);
-		}
-		else
-		{
-			waitpid(pid, NULL, 0);
-		}
-	}
-	return 1;
-}
-
-int execute(char *cmdline, char **args)
-{
-	int bg = 0, i = 0, redirect_flag = 0, pipe_num = 0;
-	pid_t pid;
-	char *redirect_filename = NULL;
-	char *redirect_args[ARGS_MAX_QUANTITY];
-	char *pipe_arg_1[ARGS_MAX_QUANTITY];
-	char *pipe_arg_2[ARGS_MAX_QUANTITY];
-
-	redirect_filename = (char *)calloc(REDIRECT_FILENAME_MAX_SIZE, sizeof(char));
-	memset(redirect_args, NULL, sizeof(redirect_args));
-
-	bg = parseline(cmdline, args);
-	redirect_flag = check_redirect(args, redirect_filename, redirect_args);
-	pipe_num = check_pipe(args, pipe_arg_1, pipe_arg_2);
-
-	if (args[0] == NULL)
-	{
-		return 1;
-	}
-	if (pipe_num == 0) /* no pipe */
-	{
-		if (!built_in(args)) /* built-in cmd? */
-		{
-			if (redirect_flag != 0) /* redirection? */
-			{
-				return do_redirect(redirect_flag, redirect_filename, redirect_args);
-			}
-			else
-			{
-				return do_bg_fg(args, bg);
-			}
-		}
-		else
-		{
-			return 1;
-		}
-	}
-	else
-	{
-		return do_pipe(pipe_arg_1, pipe_arg_2);
-	}
-}
-
-int built_in(char **args)
-{
-	if (!strcmp(args[0], "exit"))
-	{
-		exit(0);
-	}
-	else if (!strcmp(args[0], "cd"))
-	{
-		return builtin_cd(args);
-	}
-	else if (!strcmp(args[0], "history"))
-	{
-		return builtin_history(args);
-	}
-	else if (!strcmp(args[0], "mytop"))
-	{
-		return builtin_mytop();
-	}
-	else
-	{
-		return 0;
-	}
-}
-
-int builtin_cd(char **args)
-{
-	if (args[1] == NULL)
-	{
-		return 1;
-	}
-	else
-	{
-		if (chdir(args[1]) != 0)
-		{
-			perror("yeeshell");
-		}
-		return 1;
-	}
-}
-
-int builtin_history(char **args)
-{
-	int n = 0;
-	if (args[1] == NULL)
-	{
-		n = cmdline_amount;
-	}
-	else
-	{
-		n = atoi(args[1]) < cmdline_amount ? atoi(args[1]) : cmdline_amount;
-	}
-	printf("ID\tCommandline\n");
-	for (int i = 0; i < n; i++)
-	{
-		printf("%d\t%s\n", i + 1, history[i]);
-	}
-	return 1;
-}
-
-int builtin_mytop()
-{
-
-	int cputimemode = 1;
-	mytop_memory();
-	getkinfo();
-	get_procs();
-	if (prev_proc == NULL)
-		get_procs();
-	print_procs(prev_proc, proc, cputimemode);
-
-	return 1;
-}
-
-void mytop_memory()
-{
-	FILE *fp = NULL;
-	int pagesize;
-	long total = 0, free = 0, cached = 0;
-
-	if ((fp = fopen("/proc/meminfo", "r")) == NULL)
-	{
-		exit(0);
-	}
-
-	fscanf(fp, "%u %lu %lu %lu", &pagesize, &total, &free, &cached);
-	fclose(fp);
-
-	printf("memory(KBytes):\t%ld total\t%ld free\t%ld cached\n", (pagesize * total) / 1024, (pagesize * free) / 1024, (pagesize * cached) / 1024);
-
-	return;
-}
-
-void get_procs()
-{
-	struct proc *p;
-	int i;
-
-	p = prev_proc;
-	prev_proc = proc;
-	proc = p;
-
-	if (proc == NULL)
-	{
-		proc = malloc(nr_total * sizeof(proc[0]));
-
-		if (proc == NULL)
-		{
-			fprintf(stderr, "Out of memory!\n");
-			exit(1);
-		}
-	}
-
-	for (i = 0; i < nr_total; i++)
-	{
-		proc[i].p_flags = 0;
-	}
-
-	parse_dir();
-}
-
-void parse_dir()
-{
-	DIR *p_dir;
-	struct dirent *p_ent;
-	pid_t pid;
-	char *end;
-
-	if ((p_dir = opendir("/proc")) == NULL)
-	{
-		perror("opendir on " _PATH_PROC);
-		exit(1);
-	}
-
-	for (p_ent = readdir(p_dir); p_ent != NULL; p_ent = readdir(p_dir))
-	{
-		pid = strtol(p_ent->d_name, &end, 10);
-
-		if (!end[0] && pid != 0)
-		{
-			parse_file(pid);
-		}
-	}
-
-	closedir(p_dir);
-}
-
-void parse_file(pid_t pid)
-{
-	char path[PATH_MAX], name[256], type, state;
-	int version, endpt, effuid;
-	unsigned long cycles_hi, cycles_lo;
-	FILE *fp;
-	struct proc *p;
-	int i;
-
-	sprintf(path, "/proc/%d/psinfo", pid);
-
-	if ((fp = fopen(path, "r")) == NULL)
-	{
-		return;
-	}
-
-	if (fscanf(fp, "%d", &version) != 1)
-	{
-		fclose(fp);
-		return;
-	}
-
-	if (version != PSINFO_VERSION)
-	{
-		fputs("procfs version mismatch!\n", stderr);
-		exit(1);
-	}
-
-	if (fscanf(fp, " %c %d", &type, &endpt) != 2)
-	{
-		fclose(fp);
-		return;
-	}
-
-	slot++;
-
-	if (slot < 0 || slot >= nr_total)
-	{
-		fprintf(stderr, "top: unreasonable endpoint number %d\n", endpt);
-		fclose(fp);
-		return;
-	}
-
-	p = &proc[slot];
-
-	if (type == TYPE_TASK)
-	{
-		p->p_flags |= IS_TASK;
-	}
-	else if (type == TYPE_SYSTEM)
-	{
-		p->p_flags |= IS_SYSTEM;
-	}
-
-	p->p_endpoint = endpt;
-	p->p_pid = pid;
-
-	if (fscanf(fp, " %255s %c %d %d %lu %*u %lu %lu",
-			   name, &state, &p->p_blocked, &p->p_priority,
-			   &p->p_user_time, &cycles_hi, &cycles_lo) != 7)
-	{
-		fclose(fp);
-		return;
-	}
-
-	strncpy(p->p_name, name, sizeof(p->p_name) - 1);
-	p->p_name[sizeof(p->p_name) - 1] = 0;
-
-	if (state != STATE_RUN)
-	{
-		p->p_flags |= BLOCKED;
-	}
-	p->p_cpucycles[0] = make64(cycles_lo, cycles_hi);
-	p->p_memory = 0L;
-
-	if (!(p->p_flags & IS_TASK))
-	{
-		int j;
-		if ((j = fscanf(fp, " %lu %*u %*u %*c %*d %*u %u %*u %d %*c %*d %*u",
-						&p->p_memory, &effuid, &p->p_nice)) != 3)
-		{
-
-			fclose(fp);
-			return;
-		}
-
-		p->p_effuid = effuid;
-	}
-	else
-		p->p_effuid = 0;
-
-	for (i = 1; i < CPUTIMENAMES; i++)
-	{
-		if (fscanf(fp, " %lu %lu",
-				   &cycles_hi, &cycles_lo) == 2)
-		{
-			p->p_cpucycles[i] = make64(cycles_lo, cycles_hi);
-		}
-		else
-		{
-			p->p_cpucycles[i] = 0;
-		}
-	}
-
-	if ((p->p_flags & IS_TASK))
-	{
-		if (fscanf(fp, " %lu", &p->p_memory) != 1)
-		{
-			p->p_memory = 0;
-		}
-	}
-
-	p->p_flags |= USED;
-
-	fclose(fp);
-}
-
-void getkinfo()
-{
-	FILE *fp;
-
-	if ((fp = fopen("/proc/kinfo", "r")) == NULL)
-	{
-		fprintf(stderr, "opening " _PATH_PROC "kinfo failed\n");
-		exit(1);
-	}
-
-	if (fscanf(fp, "%u %u", &nr_procs, &nr_tasks) != 2)
-	{
-		fprintf(stderr, "reading from " _PATH_PROC "kinfo failed\n");
-		exit(1);
-	}
-
-	fclose(fp);
-
-	nr_total = (int)(nr_procs + nr_tasks);
-}
-
-void print_procs(struct proc *proc1, struct proc *proc2, int cputimemode)
-{
-	int p, nprocs;
-	u64_t systemticks = 0;
-	u64_t userticks = 0;
-	u64_t total_ticks = 0;
-	int blockedseen = 0;
-	static struct tp *tick_procs = NULL;
-
-	if (tick_procs == NULL)
-	{
-		tick_procs = malloc(nr_total * sizeof(tick_procs[0]));
-
-		if (tick_procs == NULL)
-		{
-			fprintf(stderr, "Out of memory!\n");
-			exit(1);
-		}
-	}
-
-	for (p = nprocs = 0; p < nr_total; p++)
-	{
-		u64_t uticks;
-		if (!(proc2[p].p_flags & USED))
-		{
-			continue;
-		}
-		tick_procs[nprocs].p = proc2 + p;
-		tick_procs[nprocs].ticks = cputicks(&proc1[p], &proc2[p], cputimemode);
-		uticks = cputicks(&proc1[p], &proc2[p], 1);
-		total_ticks = total_ticks + uticks;
-
-		if (!(proc2[p].p_flags & IS_TASK))
-		{
-			if (proc2[p].p_flags & IS_SYSTEM)
-			{
-				systemticks = systemticks + tick_procs[nprocs].ticks;
-			}
-			else
-			{
-				userticks = userticks + tick_procs[nprocs].ticks;
-			}
-		}
-
-		nprocs++;
-	}
-
-	if (total_ticks == 0)
-	{
-		return;
-	}
-
-	printf("CPU states: %6.2f%% user\t", 100.0 * userticks / total_ticks);
-	printf("%6.2f%% syst\t", 100.0 * systemticks / total_ticks);
-	printf("%6.2f%% in total\n", 100.0 * (systemticks + userticks) / total_ticks);
-}
-
-u64_t cputicks(struct proc *p1, struct proc *p2, int timemode)
-{
-	int i;
-	u64_t t = 0;
-	for (i = 0; i < CPUTIMENAMES; i++)
-	{
-		if (!CPUTIME(timemode, i))
-		{
-			continue;
-		}
-		if (p1->p_endpoint == p2->p_endpoint)
-		{
-			t = t + p2->p_cpucycles[i] - p1->p_cpucycles[i];
-		}
-		else
-		{
-			t = t + p2->p_cpucycles[i];
-		}
-	}
-
-	return t;
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include <dirent.h>
+#include <signal.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <termcap.h>
+#include <termios.h>
+#include <curses.h>
+#include <limits.h>
+#include <pwd.h>
+#include <assert.h>
+
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <sys/stat.h>
+#include <sys/times.h>
+#include <sys/time.h>
+#include <sys/select.h>
+
+#include <minix/com.h>
+#include <minix/config.h>
+#include <minix/type.h>
+#include <minix/endpoint.h>
+#include <minix/const.h>
+#include <minix/u64.h>
+#include <minix/procfs.h>
+#include <paths.h>
+
+#include "yeeshell.h"
+
+/* record cmdline history */
+char *history[CMDLINE_HISTORY_MAX_QUANTITY];
+int cmdline_amount = 0;
+
+struct proc *proc = NULL, *prev_proc = NULL;
+int order = ORDER_CPU;
+int blockedverbose = 0;
+int nr_total = 0;
+int slot = 1;
+unsigned int nr_procs, nr_tasks;
+
+int main()
+{
+	char *cmdline = NULL, *pwd = NULL;
+	char *args[ARGS_MAX_QUANTITY];
+	int status = 1;
+	pwd = (char *)calloc(PATH_MAX_SIZE, sizeof(char));
+	for (int i = 0; i < CMDLINE_HISTORY_MAX_QUANTITY; i++)
+	{
+		history[i] = (char *)calloc(CMDLINE_MAX_SIZE, sizeof(char));
+	}
+
+	/* execute the shell's read, parse and execution loop */
+	do
+	{
+		if (!getcwd(pwd, PATH_MAX_SIZE))
+		{
+			printf("yeeshell: The current path cannot be obtained!\n");
+			exit(0);
+		}
+		printf("[root@yeeshell %s]# ", pwd);
+		cmdline = readline();
+		strcpy(history[cmdline_amount++], cmdline);
+		status = execute(cmdline, args);
+		free(cmdline);
+	} while (status);
+	for (int i = 0; i < CMDLINE_HISTORY_MAX_QUANTITY; i++)
+	{
+		free(history[i]);
+	}
+	exit(EXIT_SUCCESS);
+}
+
+char *readline()
+{
+	char *cmdline = NULL;
+	ssize_t bufsize = 0;
+	getline(&cmdline, &bufsize, stdin); /* getline(<char array>，<number>，<file descriptor>) */
+	return cmdline;
+}
+
+int parseline(char *cmdline, char **args)
+{
+	static char array[CMDLINE_MAX_SIZE]; /* holds local copy of command line */
+	char *buf = array;					 /* ptr that traverses command line */
+	char *delim;						 /* points to first space delimiter */
+	int argc;							 /* number of args */
+	int bg;								 /* background job? */
+
+	strcpy(buf, cmdline);
+	buf[strlen(buf) - 1] = ' ';	  /* replace trailing '\n' with space */
+	while (*buf && (*buf == ' ')) /* ignore leading spaces */
+	{
+		buf++;
+	}
+
+	/* Build the argv list */
+	argc = 0;
+	if (*buf == '\'')
+	{
+		buf++;
+		delim = strchr(buf, '\''); /* strchr - To find the first match of a given character in a string */
+	}
+	else
+	{
+		delim = strchr(buf, ' ');
+	}
+
+	while (delim)
+	{
+		args[argc++] = buf;
+		*delim = '\0';
+		buf = delim + 1;
+		while (*buf && (*buf == ' ')) /* ignore spaces */
+		{
+			buf++;
+		}
+
+		if (*buf == '\'')
+		{
+			buf++;
+			delim = strchr(buf, '\'');
+		}
+		else
+		{
+			delim = strchr(buf, ' ');
+		}
+	}
+	args[argc] = NULL;
+
+	if (argc == 0) /* ignore blank line */
+	{
+		return 1;
+	}
+
+	/* should the job run in the background? */
+	if ((bg = (*args[argc - 1] == '&')) != 0)
+	{
+		args[--argc] = NULL;
+	}
+	return bg;
+}
+
+int check_redirect(char **args, char *redirect_filename, char **redirect_args)
+{
+	int i = 0, j = 0, redirect_flag = REDIRECT_NO;
+	while (args[i] != NULL)
+	{
+		if (!strcmp(args[i], ">"))
+		{
+			redirect_flag = REDIRECT_OUT;
+			break;
+		}
+		else if (!strcmp(args[i], "<"))
+		{
+			redirect_flag = REDIRECT_IN;
+			break;
+		}
+		i++;
+	}
+
+	if ((redirect_flag == 1) || (redirect_flag == 2))
+	{
+		strcpy(redirect_filename, args[i + 1]);
+		for (j = 0; j < i; j++)
+		{
+			redirect_args[j] = args[j];
+		}
+	}
+
+	return redirect_flag;
+}
+
+int do_redirect(int redirect_flag, char *redirect_filename, char **redirect_args)
+{
+	pid_t pid;
+	int fd = 1;
+	if ((pid = fork()) == 0) /* Child process */
+	{
+		if (redirect_flag == 1) /* out */
+		{
+			fd = open(redirect_filename, O_CREAT | O_WRONLY | O_TRUNC, S_IRUSR | S_IWUSR | S_IXUSR);
+			close(1);
+			dup(fd);
+		}
+		else if (redirect_flag == 2) /* in */
+		{
+			fd = open(redirect_filename, O_RDONLY, S_IRUSR);
+			close(0);
+			dup(fd);
+		}
+		if (execvp(redirect_args[0], redirect_args) <= 0)
+		{
+			printf("%s: Command not found\n", redirect_args[0]);
+			exit(0);
+		}
+		close(fd);
+	}
+	else /* parent process */
+	{
+		waitpid(pid, NULL, 0);
+	}
+	return 1;
+}
+
+int check_pipe(char **args, char **pipe_arg_1, char **pipe_arg_2)
+{
+	int pipe_flag = 0, i = 0, j = 0;
+
+	while (args[i] != NULL)
+	{
+		if (!strcmp(args[i], "|"))
+		{
+			pipe_flag = 1;
+			break;
+		}
+		pipe_arg_1[j++] = args[i++];
+	}
+	pipe_arg_1[j] = NULL;
+
+	j = 0;
+	i++;
+	while (args[i] != NULL)
+	{
+		pipe_arg_2[j++] = args[i++];
+	}
+	pipe_arg_2[j] = NULL;
+	return pipe_flag;
+}
+
+int do_pipe(char **pipe_arg_1, char **pipe_arg_2)
+{
+	int fds[2];
+	pipe(fds);
+	pid_t prog_1, prog_2;
+
+	if ((prog_1 = fork()) == 0) /* Child process 1 */
+	{
+		close(1);
+		dup(fds[1]);
+		close(fds[0]);
+		close(fds[1]);
+
+		if (execvp(pipe_arg_1[0], pipe_arg_1) <= 0)
+		{
+			printf("%s: Command not found\n", pipe_arg_1[0]);
+			exit(0);
+		}
+	}
+
+	if ((prog_2 = fork()) == 0) /* Child process 2 */
+	{
+		close(0);
+		dup(fds[0]);
+		close(fds[0]);
+		close(fds[1]);
+
+		if (execvp(pipe_arg_2[0], pipe_arg_2) <= 0)
+		{
+			printf("%s: Command not found\n", pipe_arg_2[0]);
+			exit(0);
+		}
+	}
+
+	close(fds[0]);
+	close(fds[1]);
+
+	waitpid(prog_1, NULL, 0);
+	waitpid(prog_2, NULL, 0);
+	return 1;
+}
+
+int do_bg_fg(char **args, int bg)
+{
+	pid_t pid;
+	if ((pid = fork()) == 0)
+	{
+		if (bg)
+		{
+			int fd = open("/dev/null", O_RDWR);
+			dup2(fd, 0);
+			dup2(fd, 1);
+		}
+		if (execvp(args[0], args) <= 0)
+		{
+			printf("%s: Command not found\n", args[0]);
+		}
+		exit(0);
+	}
+	else
+	{
+		if (bg)
+		{
+			signal(SIGCHLD, SIG_IGN);
+		}
+		else
+		{
+			waitpid(pid, NULL, 0);
+		}
+	}
+	return 1;
+}
+
+int execute(char *cmdline, char **args)
+{
+	int bg = 0, i = 0, redirect_flag = 0, pipe_num = 0;
+	pid_t pid;
+	char *redirect_filename = NULL;
+	char *redirect_args[ARGS_MAX_QUANTITY];
+	char *pipe_arg_1[ARGS_MAX_QUANTITY];
+	char *pipe_arg_2[ARGS_MAX_QUANTITY];
+
+	redirect_filename = (char *)calloc(REDIRECT_FILENAME_MAX_SIZE, sizeof(char));
+	memset(redirect_args, NULL, sizeof(redirect_args));
+
+	bg = parseline(cmdline, args);
+	redirect_flag = check_redirect(args, redirect_filename, redirect_args);
+	pipe_num = check_pipe(args, pipe_arg_1, pipe_arg_2);
+
+	if (args[0] == NULL)
+	{
+		return 1;
+	}
+	if (pipe_num == 0) /* no pipe */
+	{
+		if (!built_in(args)) /* built-in cmd? */
+		{
+			if (redirect_flag != 0) /* redirection? */
+			{
+				return do_redirect(redirect_flag, redirect_filename, redirect_args);
+			}
+			else
+			{
+				return do_bg_fg(args, bg);
+			}
+		}
+		else
+		{
+			return 1;
+		}
+	}
+	else
+	{
+		return do_pipe(pipe_arg_1, pipe_arg_2);
+	}
+}
+
+int built_in(char **args)
+{
+	if (!strcmp(args[0], "exit"))
+	{
+		exit(0);
+	}
+	else if (!strcmp(args[0], "cd"))
+	{
+		return builtin_cd(args);
+	}
+	else if (!strcmp(args[0], "history"))
+	{
+		return builtin_history(args);
+	}
+	else if (!strcmp(args[0], "mytop"))
+	{
+		return builtin_mytop();
+	}
+	else
+	{
+		return 0;
+	}
+}
+
+int builtin_cd(char **args)
+{
+	if (args[1] == NULL)
+	{
+		return 1;
+	}
+	else
+	{
+		if (chdir(args[1]) != 0)
+		{
+			perror("yeeshell");
+		}
+		return 1;
+	}
+}
+
+int builtin_history(char **args)
+{
+	int n = 0;
+	if (args[1] == NULL)
+	{
+		n = cmdline_amount;
+	}
+	else
+	{
+		n = atoi(args[1]) < cmdline_amount ? atoi(args[1]) : cmdline_amount;
+	}
+	printf("ID\tCommandline\n");
+	for (int i = 0; i < n; i++)
+	{
+		printf("%d\t%s\n", i + 1, history[i]);
+	}
+	return 1;
+}
+
+int builtin_mytop()
+{
+
+	int cputimemode = 1;
+	mytop_memory();
+	getkinfo();
+	get_procs();
+	if (prev_proc == NULL)
+		get_procs();
+	print_procs(prev_proc, proc, cputimemode);
+
+	return 1;
+}
+
+void mytop_memory()
+{
+	FILE *fp = NULL;
+	int pagesize;
+	long total = 0, free = 0, cached = 0;
+
+	if ((fp = fopen("/proc/meminfo", "r")) == NULL)
+	{
+		exit(0);
+	}
+
+	fscanf(fp, "%u %lu %lu %lu", &pagesize, &total, &free, &cached);
+	fclose(fp);
+
+	printf("memory(KBytes):\t%ld total\t%ld free\t%ld cached\n", (pagesize * total) / 1024, (pagesize * free) / 1024, (pagesize * cached) / 1024);
+
+	return;
+}
+
+void get_procs()
+{
+	struct proc *p;
+	int i;
+
+	p = prev_proc;
+	prev_proc = proc;
+	proc = p;
+
+	if (proc == NULL)
+	{
+		proc = malloc(nr_total * sizeof(proc[0]));
+
+		if (proc == NULL)
+		{
+			fprintf(stderr, "Out of memory!\n");
+			exit(1);
+		}
+	}
+
+	for (i = 0; i < nr_total; i++)
+	{
+		proc[i].p_flags = 0;
+	}
+
+	parse_dir();
+}
+
+void parse_dir()
+{
+	DIR *p_dir;
+	struct dirent *p_ent;
+	pid_t pid;
+	char *end;
+
+	if ((p_dir = opendir("/proc")) == NULL)
+	{
+		perror("opendir on " _PATH_PROC);
+		exit(1);
+	}
+
+	for (p_ent = readdir(p_dir); p_ent != NULL; p_ent = readdir(p_dir))
+	{
+		pid = strtol(p_ent->d_name, &end, 10);
+
+		if (!end[0] && pid != 0)
+		{
+			parse_file(pid);
+		}
+	}
+
+	closedir(p_dir);
+}
+
+void parse_file(pid_t pid)
+{
+	char path[PATH_MAX], name[256], type, state;
+	int version, endpt, effuid;
+	unsigned long cycles_hi, cycles_lo;
+	FILE *fp;
+	struct proc *p;
+	int i;
+
+	sprintf(path, "/proc/%d/psinfo", pid);
+
+	if ((fp = fopen(path, "r")) == NULL)
+	{
+		return;
+	}
+
+	if (fscanf(fp, "%d", &version) != 1)
+	{
+		fclose(fp);
+		return;
+	}
+
+	if (version != PSINFO_VERSION)
+	{
+		fputs("procfs version mismatch!\n", stderr);
+		exit(1);
+	}
+
+	if (fscanf(fp, " %c %d", &type, &endpt) != 2)
+	{
+		fclose(fp);
+		return;
+	}
+
+	slot++;
+
+	if (slot < 0 || slot >= nr_total)
+	{
+		fprintf(stderr, "top: unreasonable endpoint number %d\n", endpt);
+		fclose(fp);
+		return;
+	}
+
+	p = &proc[slot];
+
+	if (type == TYPE_TASK)
+	{
+		p->p_flags |= IS_TASK;
+	}
+	else if (type == TYPE_SYSTEM)
+	{
+		p->p_flags |= IS_SYSTEM;
+	}
+
+	p->p_endpoint = endpt;
+	p->p_pid = pid;
+
+	if (fscanf(fp, " %255s %c %d %d %lu %*u %lu %lu",
+			   name, &state, &p->p_blocked, &p->p_priority,
+			   &p->p_user_time, &cycles_hi, &cycles_lo) != 7)
+	{
+		fclose(fp);
+		return;
+	}
+
+	strncpy(p->p_name, name, sizeof(p->p_name) - 1);
+	p->p_name[sizeof(p->p_name) - 1] = 0;
+
+	if (state != STATE_RUN)
+	{
+		p->p_flags |= BLOCKED;
+	}
+	p->p_cpucycles[0] = make64(cycles_lo, cycles_hi);
+	p->p_memory = 0L;
+
+	if (!(p->p_flags & IS_TASK))
+	{
+		int j;
+		if ((j = fscanf(fp, " %lu %*u %*u %*c %*d %*u %u %*u %d %*c %*d %*u",
+						&p->p_memory, &effuid, &p->p_nice)) != 3)
+		{
+
+			fclose(fp);
+			return;
+		}
+
+		p->p_effuid = effuid;
+	}
+	else
+		p->p_effuid = 0;
+
+	for (i = 1; i < CPUTIMENAMES; i++)
+	{
+		if (fscanf(fp, " %lu %lu",
+				   &cycles_hi, &cycles_lo) == 2)
+		{
+			p->p_cpucycles[i] = make64(cycles_lo, cycles_hi);
+		}
+		else
+		{
+			p->p_cpucycles[i] = 0;
+		}
+	}
+
+	if ((p->p_flags & IS_TASK))
+	{
+		if (fscanf(fp, " %lu", &p->p_memory) != 1)
+		{
+			p->p_memory = 0;
+		}
+	}
+
+	p->p_flags |= USED;
+
+	fclose(fp);
+}
+
+void getkinfo()
+{
+	FILE *fp;
+
+	if ((fp = fopen("/proc/kinfo", "r")) == NULL)
+	{
+		fprintf(stderr, "opening " _PATH_PROC "kinfo failed\n");
+		exit(1);
+	}
+
+	if (fscanf(fp, "%u %u", &nr_procs, &nr_tasks) != 2)
+	{
+		fprintf(stderr, "reading from " _PATH_PROC "kinfo failed\n");
+		exit(1);
+	}
+
+	fclose(fp);
+
+	nr_total = (int)(nr_procs + nr_tasks);
+}
+
+void print_procs(struct proc *proc1, struct proc *proc2, int cputimemode)
+{
+	int p, nprocs;
+	u64_t systemticks = 0;
+	u64_t userticks = 0;
+	u64_t total_ticks = 0;
+	int blockedseen = 0;
+	static struct tp *tick_procs = NULL;
+
+	if (tick_procs == NULL)
+	{
+		tick_procs = malloc(nr_total * sizeof(tick_procs[0]));
+
+		if (tick_procs == NULL)
+		{
+			fprintf(stderr, "Out of memory!\n");
+			exit(1);
+		}
+	}
+
+	for (p = nprocs = 0; p < nr_total; p++)
+	{
+		u64_t uticks;
+		if (!(proc2[p].p_flags & USED))
+		{
+			continue;
+		}
+		tick_procs[nprocs].p = proc2 + p;
+		tick_procs[nprocs].ticks = cputicks(&proc1[p], &proc2[p], cputimemode);
+		uticks = cputicks(&proc1[p], &proc2[p], 1);
+		total_ticks = total_ticks + uticks;
+
+		if (!(proc2[p].p_flags & IS_TASK))
+		{
+			if (proc2[p].p_flags & IS_SYSTEM)
+			{
+				systemticks = systemticks + tick_procs[nprocs].ticks;
+			}
+			else
+			{
+				userticks = userticks + tick_procs[nprocs].ticks;
+			}
+		}
+
+		nprocs++;
+	}
+
+	if (total_ticks == 0)
+	{
+		return;
+	}
+
+	printf("CPU states: %6.2f%% user\t", 100.0 * userticks / total_ticks);
+	printf("%6.2f%% system\t", 100.0 * systemticks / total_ticks);
+	printf("%6.2f%% in total\n", 100.0 * (systemticks + userticks) / total_ticks);
+}
+
+u64_t cputicks(struct proc *p1, struct proc *p2, int timemode)
+{
+	int i;
+	u64_t t = 0;
+	for (i = 0; i < CPUTIMENAMES; i++)
+	{
+		if (!CPUTIME(timemode, i))
+		{
+			continue;
+		}
+		if (p1->p_endpoint == p2->p_endpoint)
+		{
+			t = t + p2->p_cpucycles[i] - p1->p_cpucycles[i];
+		}
+		else
+		{
+			t = t + p2->p_cpucycles[i];
+		}
+	}
+
+	return t;
 }
\ No newline at end of file