xv6-----shell

这是操作系统原理课程的第一个编程作业，补全shell的功能。

主要实现了基础的三类命令

• 可执行的程序命令
• 重定向命令
• 管道命令

实现的"基类" (原谅我用了这个词)就是struct cmd这个结构体就一个成员，用于记录命令的类型．

三类, ‘ ‘ 表示可执行程序 ‘|‘ 表示管道命令, 　‘<‘  和‘>‘　表示重定向类型．

每一个类型分别继承基类，派生出对应的三类结构体

struct execcmd

struct redircmd

struct pipecmd

void runcmd(struct cmd * cmd);

这个函数是真正驱动调用实现shell的核心．负责调用系统接口函数 execv(), open(), close(), dup(), pipe()等等一系列函数，来完成我们既定的目标．

作业也就是补全这个函数．

这是个递归的函数！

下面是来自github上的代码，仅摘录runcmd函数

 1 void
 2 runcmd(struct cmd *cmd)
 3 {
 4   int p[2]; // used for pipe line in shell
 5   int r;    // return value
 6   struct execcmd *ecmd;
 7   struct pipecmd *pcmd;
 8   struct redircmd *rcmd;
 9
10   if(cmd == 0)
11     exit(0);
12
13   switch(cmd->type){
14   default:
15     fprintf(stderr, "unknown runcmd\n");
16     exit(-1);
17
18   case ‘ ‘:
19     ecmd = (struct execcmd*)cmd;
20     if(ecmd->argv[0] == 0)
21       exit(0);
22     //fprintf(stderr, "exec not implemented\n");
23     // Your code here ...
24     if (access(ecmd->argv[0], S_IXUSR | S_IRUSR) == 0)
25     {
26         execv(ecmd->argv[0], ecmd->argv);
27     }
28     else
29     {
30         if(chdir("/bin/") < 0)
31         {
32             printf("change directory failed in line %d\n", __LINE__);
33             exit(0);
34         }
35         execv(ecmd->argv[0], ecmd->argv);
36     }
37     fprintf(stderr, "execv() %s failed in line %d\n", ecmd->argv[0], __LINE__);
38     break;
39
40   case ‘>‘:
41   case ‘<‘:
42     rcmd = (struct redircmd*)cmd;
43     //fprintf(stderr, "redir not implemented\n");
44     // Your code here ...
45     close(rcmd->fd);
46     if(open(rcmd->file, rcmd->mode) < 0)
47     {
48         fprintf(stderr, "Try to open :%s failed\n", rcmd->file);
49         exit(0);
50     }
51     runcmd(rcmd->cmd);
52     break;
53
54   case ‘|‘:
55     pcmd = (struct pipecmd*)cmd;
56     //fprintf(stderr, "pipe not implemented\n");
57     // Your code here ...
58     if(pipe(p) < 0)
59     {
60         fprintf(stderr, "call syscall pipe() failed in line %d\n", __LINE__);
61         exit(0);
62     }
63
64     if(fork1() == 0)
65     {
66         close(1);
67         dup(p[1]);
68         close(p[0]);
69         close(p[1]);
70         runcmd(pcmd->left);
71     }
72
73     if(fork1() == 0)
74     {
75         close(0);
76         dup(p[0]);
77         close(p[0]);
78         close(p[1]);
79         runcmd(pcmd->right);
80     }
81
82     close(p[0]);
83     close(p[1]);
84     wait();
85     wait();
86     break;
87   }
88
89   exit(0);
90 }

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