Add simple redirection and it can run now

- add redirect in/out/background, which is too simple
- use associativity of bison to fix shift/reduce confliction
  - in bison, we can define associativity of token by this way:

```bison

// in the first part
%locations
%left PLUS MINUS
%left TIMES DEV
%right ...
%nonassoc ...
```

    left or right means the order it is from ( we calculate lots
    of plus from the left ), while nonassoc means it has no
    associativity.

5 files changed, 196 insertions, 76 deletions

diff --git a/Makefile b/Makefile
index 8410a24..c052fe9 100644
--- a/Makefile
+++ b/Makefile
@@ -1,32 +1,14 @@
-CC = gcc
-FLEX = flex
-BISON = bison
+bcsh: syntax.tab.o bcsh.c
+        gcc -g -o bcsh bcsh.c syntax.tab.o -lfl
 
-CFILES = $(shell find . -name "*.c")
-OBJS = $(CFILES:.c=.o)
-LFILE = $(wildcard *.l)
-YFILE = $(wildcard *.y)
-LFC = ./lex.yy.c
-YFC = ./syntax.tab.c
-LFO = $(LFC:.c=.o)
-YFO = $(YFC:.c=.o)
+syntax.tab.o: lex.yy.c syntax.tab.c
+        gcc -g -c syntax.tab.c -o syntax.tab.o
 
-bcsh: syntax $(filter-out $(LFO),$(OBJS))
-        $(CC) -g -o bcsh $(filter-out $(LFO),$(OBJS)) -lfl
+lex.yy.c: lex.l
+        flex -o lex.yy.c lex.l
 
-syntax: lexical syntax-c
-        $(CC) -c $(YFC) -o $(YFO)
-
-lexical: $(LFILE)
-        $(FLEX) -o $(LFC) $(LFILE)
-
-syntax-c: $(YFILE)
-        $(BISON) -o $(YFC) -d -v $(YFILE) -Wcounterexamples
-
--include $(patsubst %.o, %.d, $(OBJS))
+syntax.tab.c: syntax.y
+        bison -o syntax.tab.c -d -v syntax.y -Wcounterexamples
 
 clean:
-        rm -f bcsh lex.yy.c syntax.tab.c syntax.tab.h syntax.output
-        rm -f $(OBJS) $(OBJS:.o=.d)
-        rm -f $(LFC) $(YFC) $(YFC:.c=.h)
-        rm -f *~
\ No newline at end of file
+        rm -f bcsh lex.yy.c syntax.tab.c syntax.tab.h syntax.output syntax.tab.o
diff --git a/bcsh.c b/bcsh.c
index 6830671..08f7ac7 100644
--- a/bcsh.c
+++ b/bcsh.c
@@ -1,40 +1,161 @@
 #include "cmd.h"
 
 extern int yyparse();
+char hostname[100];
+char *username;
+char pwd[100];
 
 int main(int argc, char **argv) {
+    // 获取当前登陆的用户名、系统主机名、当前工作路径
+    gethostname(hostname, sizeof(hostname));
+    getcwd(pwd, sizeof(pwd));
+    username = getpwuid(getuid())->pw_name;
+    showPrompt();
     while (true) {
         yyparse();
     }
     return 0;
 }
 
+void showPrompt() {
+    printf("\033[01;32m%s@%s\033[00m:\033[33m%s\033[00m$ ", username, hostname,
+           pwd);
+    // 强制刷新缓冲区
+    fflush(stdout);
+}
+
 Command *newcmd() {
     Command *cmd = (Command *)malloc(sizeof(Command));
     cmd->argc = 0;
     cmd->args = NULL;
-    cmd->type = CMD_TYPE_NORMAL;
+    cmd->type = CMD_NORMAL;
     cmd->left = NULL;
     cmd->right = NULL;
+    for (int i = 0; i < 3; i++) {
+        cmd->redirectFile[i] = NULL;
+        cmd->redirectFD[i] = i;
+    }
+    cmd->background = false;
     return cmd;
 }
 
 int runcmd(Command *cmd) {
-    int i;
+    int status;
     if (cmd == NULL) {
         fprintf(stderr, "cmd is NULL\n");
-    } else if (cmd->type != CMD_TYPE_NORMAL) {
-        runcmd(cmd->left);
-        runcmd(cmd->right);
-        return 0;
+        return -1;
     }
-    printcmd(cmd);
-    if (!strcmp(cmd->args[0], "exit")) {
-        freecmd(cmd);
-        exit(0);
+
+    if (cmd->type == CMD_NORMAL) {
+        pid_t pid;
+        if (!strcmp(cmd->args[0], "exit")) {
+            printf("Good Bye, %s!\n", username);
+            exit(0);
+        } else if (!strcmp(cmd->args[0], "cd")) {
+            if (cmd->argc == 1) {
+                chdir(getenv("HOME"));
+            } else {
+                chdir(cmd->args[1]);
+            }
+            printf("\r");
+            getcwd(pwd, sizeof(pwd));
+        } else {
+            if ((pid = fork()) == 0) {
+                // consider the redirection now
+                // it's just a part of normal command
+                // but not in other types
+                for (int i = 0; i < 3; i++) {
+                    if (cmd->redirectFD[i] != i) {
+                        close(i);
+                        dup2(cmd->redirectFD[i], i);
+                    } else if (cmd->redirectFile[i] != NULL) {
+                        int fd =
+                            open(cmd->redirectFile[i], O_RDWR | O_CREAT, 0666);
+                        if (fd < 0) {
+                            fprintf(stderr, "open file %s failed\n",
+                                    cmd->redirectFile[i]);
+                            exit(-1);
+                        }
+                        close(i);
+                        dup2(fd, i);
+                        close(fd);
+                    }
+                }
+                if (cmd->background) {
+                    setpgid(0, 0);
+                    // no output, redirect 1 and 2 to /dev/null
+                    int fd = open("/dev/null", O_RDWR);
+                    dup2(fd, 1);
+                    dup2(fd, 2);
+                    close(fd);
+                }
+                exit(execvp(cmd->args[0], cmd->args));
+            } else {
+                if (!cmd->background) {
+                    waitpid(pid, &status, 0);
+                    if (!WIFEXITED(status)) {
+                        // when here, the child process exited abnormally
+                        fprintf(stderr, "Process %d exited with status %d\n",
+                                pid, WEXITSTATUS(status));
+                    }
+                }
+            }
+            // return the exit status of the child process
+            return WEXITSTATUS(status);
+        }
+    } else if (cmd->type == CMD_PIPE) {
+        // create a pipe file and gets two file descriptors
+        // fd[0] is the read end, while fd[1] the write end
+        int fd[2];
+        pid_t left, right;
+        pipe(fd);
+        if ((left = fork()) == 0) {
+            /*
+             * close the read end of the pipe, so that the child process
+             * can only write to it; then redirect the standard output
+             * to the write end of the pipe, and close the write end
+             * itself as a file descriptor.
+             */
+            close(fd[0]);
+            dup2(fd[1], 1);
+            close(fd[1]);
+            exit(runcmd(cmd->left));
+        }
+        if ((right = fork()) == 0) {
+            close(fd[1]);
+            dup2(fd[0], 0);
+            close(fd[0]);
+            exit(runcmd(cmd->right));
+        }
+        // close the pipe, because the parent process doesn't need it
+        // and wait for the two child processes to exit
+        close(fd[0]);
+        close(fd[1]);
+        waitpid(left, NULL, 0);
+        waitpid(right, NULL, 0);
+    } else if (cmd->type == CMD_AND) {
+        if (fork() == 0) {
+            exit(runcmd(cmd->left));
+        } else {
+            waitpid(-1, &status, 0);
+            if (WIFEXITED(status) && WEXITSTATUS(status) == 0 && fork() == 0) {
+                status = runcmd(cmd->right);
+            }
+            wait(NULL);
+        }
+    } else if (cmd->type == CMD_OR) {
+        if (fork() == 0) {
+            exit(runcmd(cmd->left));
+        } else {
+            waitpid(-1, &status, 0);
+            if (WIFEXITED(status) && WEXITSTATUS(status) != 0 && fork() == 0) {
+                status = runcmd(cmd->right);
+            }
+            wait(NULL);
+        }
     }
     freecmd(cmd);
-    return 0;
+    return status;
 }
 
 void freecmd(Command *cmd) {
@@ -52,13 +173,10 @@ void freecmd(Command *cmd) {
         free(cmd->args[i]);
     }
     free(cmd->args);
-    free(cmd);
-}
-
-void printcmd(Command *cmd) {
-    int i;
-    for (i = 0; i < cmd->argc; i++) {
-        printf("%s ", cmd->args[i]);
+    for (i = 0; i < 3; i++) {
+        if (cmd->redirectFile[i] != NULL) {
+            free(cmd->redirectFile[i]);
+        }
     }
-    printf("\n");
+    free(cmd);
 }
\ No newline at end of file
diff --git a/cmd.h b/cmd.h
index 38b3fa1..d591111 100644
--- a/cmd.h
+++ b/cmd.h
@@ -1,16 +1,21 @@
 #ifndef CMD_H
 #define CMD_H
 
+#include <pwd.h>
 #include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include <fcntl.h>
 
 typedef enum {
-    CMD_TYPE_NORMAL,
-    CMD_TYPE_PIPE,
-    CMD_TYPE_AND,
-    CMD_TYPE_OR,
+    CMD_NORMAL,
+    CMD_PIPE,
+    CMD_AND,
+    CMD_OR,
     // add more command types as needed
 } CommandType;
 
@@ -20,9 +25,13 @@ typedef struct Command {
     int argc;
     struct Command *left;  // a pointer to the left sub-command
     struct Command *right; // a pointer to the right sub-command
+    int redirectFD[3];
+    char *redirectFile[3];
+    bool background;
 } Command;
 
-Command* newcmd();
+void showPrompt();
+Command *newcmd();
 int runcmd(Command *cmd);
 void freecmd(Command *cmd);
 void printcmd(Command *cmd);
diff --git a/lex.l b/lex.l
index c530ca0..3b99f1c 100644
--- a/lex.l
+++ b/lex.l
@@ -14,9 +14,11 @@ void yyerror(const char *s);
 "|"                    { return PIPE; }
 "&&"                   { return AND; }
 "||"                   { return OR; }
-\"(\\.|[^\"])*\"       { yylval.str = strdup(yytext); return STRING; }
-[a-zA-Z0-9_\-\/.]+     { yylval.str = strdup(yytext); return WORD; }
-
+"<"                    { return REDIRECT_IN; }
+">"                    { return REDIRECT_OUT; }
+"&"                    { return BACKGROUND; }
+[0-2]">"&[0-2]         { yylval.str = strdup(yytext); return FD_REDIRECT; }
+[a-zA-Z0-9_\-\/\*.]+   { yylval.str = strdup(yytext); return WORD; }
 
 %%
 
diff --git a/syntax.y b/syntax.y
index d9d3510..5f33c9a 100644
--- a/syntax.y
+++ b/syntax.y
@@ -8,14 +8,20 @@
     char *str;
     struct Command *cmd;
     CommandType cmdType;
+    int fd;
 }
 
-%token <str> WORD STRING error
-%token NEWLINE PIPE AND OR
+%token <str> WORD STRING error FD_REDIRECT
+%token NEWLINE PIPE AND OR REDIRECT_IN REDIRECT_OUT BACKGROUND
 
 %type <cmd> line command part runcommand
 %type <cmdType> separator
 
+%locations
+%nonassoc WORD
+%nonassoc BACKGROUND
+%nonassoc REDIRECT_IN REDIRECT_OUT
+
 %%
 
 line:
@@ -26,8 +32,8 @@ line:
 runcommand:
     command NEWLINE {
         $$ = $1;
-        printf("running command: \n");
         runcmd($$);
+        showPrompt();
     }
     | NEWLINE { $$ = NULL; }
     ;
@@ -44,18 +50,17 @@ command:
     }
     ;
 
+separator:
+    PIPE { $$ = CMD_PIPE; }
+    | AND { $$ = CMD_AND; }
+    | OR { $$ = CMD_OR; }
+    ;
+
 part:
     part WORD {
         $$ = $1;
         $$->argc++;
-        $$->args = realloc($$->args, ($$->argc) * sizeof(char *));
-        $$->args[$$->argc - 1] = $2;
-        $$->args[$$->argc] = NULL;
-    }
-    | part STRING {
-        $$ = $1;
-        $$->argc++;
-        $$->args = realloc($$->args, ($$->argc) * sizeof(char *));
+        $$->args = realloc($$->args, ($$->argc + 1) * sizeof(char *));
         $$->args[$$->argc - 1] = $2;
         $$->args[$$->argc] = NULL;
     }
@@ -65,18 +70,22 @@ part:
         $$->args[$$->argc++] = $1;
         $$->args[$$->argc] = NULL;
     }
-    | STRING {
-        $$ = newcmd();
-        $$->args = malloc(2 * sizeof(char *));
-        $$->args[$$->argc++] = $1;
-        $$->args[$$->argc] = NULL;
+    | part REDIRECT_IN WORD {
+        $$ = $1;
+        $$->redirectFile[0] = $3;
+    }
+    | part REDIRECT_OUT WORD {
+        $$ = $1;
+        $$->redirectFile[1] = $3;
+    }
+    | part FD_REDIRECT {
+        $$ = $1;
+        $$->redirectFD[$2[0]-'0']=$2[3]-'0';
+    }
+    | part BACKGROUND {
+        $$ = $1;
+        $$->background = true;
     }
-    ;
-
-separator:
-    PIPE { $$ = CMD_TYPE_PIPE; }
-    | AND { $$ = CMD_TYPE_AND; }
-    | OR { $$ = CMD_TYPE_OR; }
     ;
 
 %%