diff --git a/yeeshell b/yeeshell
index cbf51a2..ba5008e 100755
Binary files a/yeeshell and b/yeeshell differ
diff --git a/yeeshell.c b/yeeshell.c
index 4338544..ae5ff24 100644
--- a/yeeshell.c
+++ b/yeeshell.c
@@ -2,15 +2,20 @@
 #include <stdlib.h>
 #include <sys/types.h>
 #include <sys/wait.h>
+#include <sys/stat.h>
 #include <unistd.h>
 #include <string.h>
 #include <dirent.h>
+#include <errno.h>
 #include "yeeshell.h"
 
 /* record cmdline history */
-char **history = NULL;
+char *history[CMDLINE_HISTORY_MAX_QUANTITY];
 int cmdline_amount = 0;
 
+/* if true, print additional output */
+int verbose = 0;
+
 /* next job ID to allocate */
 int nextjid = 1;
 
@@ -26,12 +31,21 @@ int main()
 	char *args[ARGS_MAX_QUANTITY];
 	int status = 1;
 	pwd = (char *)calloc(PATH_MAX, sizeof(char));
-	if (!(history = (char **)calloc(CMDLINE_HISTORY_MAX_QUANTITY, CMDLINE_MAX_SIZE * sizeof(char *))))
+	for (int i = 0; i < CMDLINE_HISTORY_MAX_QUANTITY; i++)
 	{
-		printf("yeeshell: allocation error!\n");
-		exit(EXIT_FAILURE);
+		history[i] = (char *)calloc(CMDLINE_MAX_SIZE, sizeof(char));
 	}
+	/* Install the signal handlers */
+
+	/* These are the ones you will need to implement */
+	Signal(SIGINT, sigint_handler);	  /* ctrl-c */
+	Signal(SIGTSTP, sigtstp_handler); /* ctrl-z */
+	Signal(SIGCHLD, sigchld_handler); /* Terminated or stopped child */
+
+	/* This one provides a clean way to kill the shell */
+	Signal(SIGQUIT, sigquit_handler);
 
+	initjobs(jobs);
 	/* execute the shell's read, parse and execution loop */
 	do
 	{
@@ -40,13 +54,16 @@ int main()
 			printf("yeeshell: The current path cannot be obtained!\n");
 			exit(0);
 		}
-		printf("[yeeshell %s]# ", pwd);
+		printf("[root@yeeshell %s]# ", pwd);
 		cmdline = readline();
-		history[cmdline_amount++] = cmdline;
+		strcpy(history[cmdline_amount++], cmdline);
 		status = execute(cmdline, args);
 		free(cmdline);
 	} while (status);
-	free(history);
+	for (int i = 0; i < CMDLINE_HISTORY_MAX_QUANTITY; i++)
+	{
+		free(history[i]);
+	}
 	exit(EXIT_SUCCESS);
 }
 
@@ -147,7 +164,7 @@ int execute(char *cmdline, char **args)
 			/* Set the pid of the current process to the group number of the process group it belongs to. */
 			/* avoid being grouped with tsh */
 			setpgid(0, 0);
-			if (execve(args[0], args, environ) <= 0)
+			if (execvp(args[0], args) <= 0)
 			{
 				printf("%s: Command not found\n", args[0]);
 				exit(0);
@@ -201,17 +218,13 @@ int built_in(char **args)
 	{
 		return builtin_mytop(args);
 	}
-	else if (!strcmp(args[0], "ls"))
-	{
-		return builtin_ls(args);
-	}
 	else if (!strcmp(args[0], "jobs"))
 	{
 		return builtin_jobs(args);
 	}
 	else
 	{
-		return -1;
+		return 0;
 	}
 }
 
@@ -231,39 +244,21 @@ int builtin_cd(char **args)
 	}
 }
 
-int builtin_ls(char **args)
+int builtin_history(char **args)
 {
-	DIR *dp;
-	struct dirent *dirp;
-	char *path = NULL;
-
+	int n = 0;
 	if (args[1] == NULL)
 	{
-		path = (char *)calloc(PATH_MAX, sizeof(char));
-		getcwd(path, PATH_MAX)
+		n = cmdline_amount;
 	}
-	else if (args[1])
-
-		if ((dp = opendir(args[1])) == NULL)
-		{
-			perror("yeeshell");
-		}
-	while ((dirp = readdir(dp)) != NULL)
+	else
 	{
-		printf("%s\n", dirp->d_name);
+		n = atoi(args[1]) < cmdline_amount ? atoi(args[1]) : cmdline_amount;
 	}
-
-	closedir(dp);
-	return 0;
-}
-
-int builtin_history(char **args)
-{
-	int n = atoi(args[1]);
 	printf("ID\tCommandline\n");
-	for (int i = 0; i < ((n < cmdline_amount) ? n : cmdline_amount); i++)
+	for (int i = 0; i < n; i++)
 	{
-		printf("%d\t%s\n", i, history[i]);
+		printf("%d\t%s\n", i + 1, history[i]);
 	}
 	return 1;
 }
@@ -309,11 +304,98 @@ int builtin_mytop(char **args)
 
 int do_bgfg(char **args)
 {
+	/* initialize variables */
+	struct job_t *currentJob;
+	int jid;
+	pid_t pid;
+	sigset_t mask_all, mask_prev;
+	sigfillset(&mask_all);
+
+	sigprocmask(SIG_SETMASK, &mask_all, &mask_prev);
+
+	/* bg or fg has the argument? */
+	if (args[1] == NULL)
+	{
+		printf("%s command requires PID or %%jobid argument\n", args[0]);
+		return 1;
+	}
+	/* if process by jid, gets the corresponding Job structure*/
+	else if (args[1][0] == '%')
+	{
+		jid = atoi(args[1][1]);
+		currentJob = getjobjid(jobs, jid);
+		if (currentJob == NULL)
+		{
+			printf("%%%d: No such job\n", jid);
+			return 1;
+		}
+		pid = currentJob->pid;
+	}
+	/* if process by pid, gets the corresponding Job structure */
+	else
+	{
+		pid = atoi(args[1]);
+		currentJob = getjobpid(jobs, pid);
+		if (pid <= 0)
+		{
+			printf("%s: argument must be a PID or %%jobid\n", args[0]);
+			return 1;
+		}
+		currentJob = getjobpid(jobs, pid);
+		if (currentJob == NULL)
+		{
+			printf("(%d): No such process\n", pid);
+			return 1;
+		}
+	}
+
+	/* bg or fg? */
+	if (!strcmp(args[0], "bg")) /* if bg */
+	{
+		currentJob->state = BG;
+		printf("[%d] (%d) %s", currentJob->jid, pid, currentJob->cmdline);
+		sigprocmask(SIG_SETMASK, &mask_prev, NULL);
+		kill(-pid, SIGCONT); /* send the SIGCONT to the pid */
+		return 1;
+	}
+	else if (!strcmp(args[0], "fg")) /* if fg */
+	{
+		currentJob->state = FG;
+		sigprocmask(SIG_SETMASK, &mask_prev, NULL);
+		kill(-pid, SIGCONT);	 /* send the SIGCONT to the pid */
+		waitfg(currentJob->pid); /* Child process switched to FG, so wait for it to finish */
+		return 1;
+	}
+	else if (!strcmp(args[0], "kill"))
+	{
+		sigprocmask(SIG_SETMASK, &mask_prev, NULL);
+		kill(-pid, SIGQUIT);
+		return 1;
+	}
+	return 1;
+}
+
+void waitfg(pid_t pid)
+{
+	sigset_t m;
+	sigemptyset(&m);
+	while (pid == fgpid(jobs))
+	{
+		/* Wake up when there is a signal to check whether the foreground process PID change, */
+		/* change means that the foreground process is over. */
+		sigsuspend(&m);
+	}
+	return;
+}
+
+void initjobs(struct job_t *jobs)
+{
+	int i;
+
+	for (i = 0; i < JOBS_MAX_QUANTITY; i++)
+		clearjob(&jobs[i]);
 }
 
-/************************
- * manipulate job list  
- ************************/
 int addjob(struct job_t *jobs, pid_t pid, int state, char *cmdline)
 {
 	int i;
@@ -332,8 +414,10 @@ int addjob(struct job_t *jobs, pid_t pid, int state, char *cmdline)
 				nextjid = 1;
 			strcpy(jobs[i].cmdline, cmdline);
 
-			printf("Added job [%d] %d %s\n", jobs[i].jid, jobs[i].pid, jobs[i].cmdline);
-
+			if (verbose)
+			{
+				printf("Added job [%d] %d %s\n", jobs[i].jid, jobs[i].pid, jobs[i].cmdline);
+			}
 			return 1;
 		}
 	}
@@ -341,20 +425,6 @@ int addjob(struct job_t *jobs, pid_t pid, int state, char *cmdline)
 	return 0;
 }
 
-int pid2jid(pid_t pid)
-{
-	int i;
-
-	if (pid < 1)
-		return 0;
-	for (i = 0; i < JOBS_MAX_QUANTITY; i++)
-		if (jobs[i].pid == pid)
-		{
-			return jobs[i].jid;
-		}
-	return 0;
-}
-
 void listjobs(struct job_t *jobs)
 {
 	for (int i = 0; i < JOBS_MAX_QUANTITY; i++)
@@ -381,17 +451,45 @@ void listjobs(struct job_t *jobs)
 	}
 }
 
-void waitfg(pid_t pid)
+int deletejob(struct job_t *jobs, pid_t pid)
 {
-	sigset_t m;
-	sigemptyset(&m);
-	while (pid == fgpid(jobs))
+	int i;
+
+	if (pid < 1)
+		return 0;
+
+	for (i = 0; i < JOBS_MAX_QUANTITY; i++)
 	{
-		/* Wake up when there is a signal to check whether the foreground process PID change, */
-		/* change means that the foreground process is over. */
-		sigsuspend(&m);
+		if (jobs[i].pid == pid)
+		{
+			clearjob(&jobs[i]);
+			nextjid = maxjid(jobs) + 1;
+			return 1;
+		}
 	}
-	return;
+	return 0;
+}
+
+void clearjob(struct job_t *job)
+{
+	job->pid = 0;
+	job->jid = 0;
+	job->state = UNDF;
+	job->cmdline[0] = '\0';
+}
+
+int pid2jid(pid_t pid)
+{
+	int i;
+
+	if (pid < 1)
+		return 0;
+	for (i = 0; i < JOBS_MAX_QUANTITY; i++)
+		if (jobs[i].pid == pid)
+		{
+			return jobs[i].jid;
+		}
+	return 0;
 }
 
 pid_t fgpid(struct job_t *jobs)
@@ -402,14 +500,92 @@ pid_t fgpid(struct job_t *jobs)
 	return 0;
 }
 
-int hide(const char *path)
+struct job_t *getjobpid(struct job_t *jobs, pid_t pid)
 {
-	if (*path == '.')
+	int i;
+
+	if (pid < 1)
+		return NULL;
+	for (i = 0; i < JOBS_MAX_QUANTITY; i++)
+		if (jobs[i].pid == pid)
+			return &jobs[i];
+	return NULL;
+}
+
+struct job_t *getjobjid(struct job_t *jobs, int jid)
+{
+	int i;
+
+	if (jid < 1)
+		return NULL;
+	for (i = 0; i < JOBS_MAX_QUANTITY; i++)
+		if (jobs[i].jid == jid)
+			return &jobs[i];
+	return NULL;
+}
+
+handler_t *Signal(int signum, handler_t *handler)
+{
+	struct sigaction action, old_action;
+
+	action.sa_handler = handler;
+	sigemptyset(&action.sa_mask); /* block sigs of type being handled */
+	action.sa_flags = SA_RESTART; /* restart syscalls if possible */
+
+	if (sigaction(signum, &action, &old_action) < 0)
+		fprintf(stdout, "%s: %s\n", 'Signal Error', strerror(errno));
+	return (old_action.sa_handler);
+}
+
+void sigchld_handler(int signal)
+{
+	pid_t pid;
+	int status;
+	while ((pid = waitpid(-1, &status, WNOHANG | WUNTRACED)) > 0)
 	{
-		return 1;
+		if (WIFEXITED(status)) /* Normal termination */
+		{
+			deletejob(jobs, pid);
+		}
+		if (WIFSTOPPED(status)) /* Task suspension */
+		{
+			struct job_t *job = getjobpid(jobs, pid);
+			int jid = pid2jid(pid);
+			printf("Job [%d] (%d) stopped by signal %d\n", jid, pid, WSTOPSIG(status));
+			job->state = ST;
+		}
+		if (WIFSIGNALED(status)) /* Task terminated */
+		{
+			int jid = pid2jid(pid);
+			printf("Job [%d] (%d) terminated by signal %d\n", jid, pid, WTERMSIG(status));
+			deletejob(jobs, pid);
+		}
 	}
-	else
+	return;
+}
+
+void sigint_handler(int signal)
+{
+	pid_t pid = fgpid(jobs);
+	if (pid != 0)
 	{
-		return 0;
+		kill(-pid, signal);
 	}
+	return;
+}
+
+void sigtstp_handler(int signal)
+{
+	pid_t pid = fgpid(jobs);
+	if (pid > 0)
+	{
+		kill(-pid, signal);
+	}
+	return;
+}
+
+void sigquit_handler(int signal)
+{
+	printf("Terminating after receipt of SIGQUIT signal\n");
+	exit(1);
 }
\ No newline at end of file
diff --git a/yeeshell.h b/yeeshell.h
index a3ef706..b1c2152 100644
--- a/yeeshell.h
+++ b/yeeshell.h
@@ -7,10 +7,12 @@
 #define CMDLINE_HISTORY_MAX_QUANTITY 256
 #define JOBS_MAX_QUANTITY 16
 #define PATH_MAX_SIZE 256
+#define LS_BUF_SIZE 1024
 
-#define FG 1 /* running in foreground */
-#define BG 2 /* running in background */
-#define ST 3 /* stopped */
+#define UNDF 0 /* undefined */
+#define FG 1   /* running in foreground */
+#define BG 2   /* running in background */
+#define ST 3   /* stopped */
 
 /* job_t - The job struct */
 struct job_t
@@ -33,7 +35,6 @@ int execute(char *cmdline, char **args);
 /* builtin functions - Handle built-in command */
 int built_in(char **args);
 int builtin_cd(char **args);
-int builtin_ls(char **args);
 int builtin_history(char **args);
 int builtin_jobs(char **args);
 int builtin_mytop(char **args);
@@ -41,19 +42,66 @@ int builtin_mytop(char **args);
 /* do_bgfg - Execute background/foregroung tasks */
 int do_bgfg(char **args);
 
+/* waitfg - Wait foreground jobs to finish */
+void waitfg(pid_t pid);
+
+/* initjobs - Initialize the job list */
+void initjobs(struct job_t *jobs);
+
 /* addjob - Add jobs to joblist */
 int addjob(struct job_t *jobs, pid_t pid, int state, char *cmdline);
 
+/* listjobs - Print the job list */
+void listjobs(struct job_t *jobs);
+
+/* deletejob - Delete a job whose PID=pid from the job list */
+int deletejob(struct job_t *jobs, pid_t pid);
+
+/* clearjob - Clear the entries in a job struct */
+void clearjob(struct job_t *job);
+
 /* pide2jid - Map process ID to job ID*/
 int pid2jid(pid_t pid);
 
-/* waitfg - Wait foreground jobs to finish */
-void waitfg(pid_t pid);
-
 /* fgpid - Return PID of current foreground job, 0 if no such job */
 pid_t fgpid(struct job_t *jobs);
 
-/* determine if a file is hidden */
-int hide(const char *path);
+/* getjobpid - Find a job (by PID) on the job list */
+struct job_t *getjobpid(struct job_t *jobs, pid_t pid);
+
+/* getjobjid  - Find a job (by JID) on the job list */
+struct job_t *getjobjid(struct job_t *jobs, int jid);
+
+/* Signal - wrapper for the sigaction function */
+typedef void handler_t(int);
+handler_t *Signal(int signum, handler_t *handler);
+
+/* 
+ * sigchld_handler - The kernel sends a SIGCHLD to the shell whenever
+ *     a child job terminates (becomes a zombie), or stops because it
+ *     received a SIGSTOP or SIGTSTP signal. The handler reaps all
+ *     available zombie children, but doesn't wait for any other
+ *     currently running children to terminate.  
+ */
+void sigchld_handler(int signal);
+
+/* 
+ * sigint_handler - The kernel sends a SIGINT to the shell whenver the
+ *    user types ctrl-c at the keyboard.  Catch it and send it along
+ *    to the foreground job.  
+ */
+void sigint_handler(int signal);
+
+/*
+ * sigtstp_handler - The kernel sends a SIGTSTP to the shell whenever
+ *     the user types ctrl-z at the keyboard. Catch it and suspend the
+ *     foreground job by sending it a SIGTSTP.  
+ */
+
+void sigtstp_handler(int signal);
 
-/*  */
\ No newline at end of file
+/*
+ * sigquit_handler - The driver program can gracefully terminate the
+ *    child shell by sending it a SIGQUIT signal.
+ */
+void sigquit_handler(int signal);
\ No newline at end of file