第4章 文件和目录_贯穿案例2：mini shell

Posted 2020-08-29 浅墨浓香

6. 贯穿案例2：mini shell（1）

【阶段性任务】实现cd、pwd和quit命令

 

//job.h

#ifndef __JOB_H__
#define __JOB_H__

//接收命令行参数
typedef struct
{
    char** args;  //对应于主函数中的char* argv[]参数（含进程名本身）
}Program;

//命令行中可以包含多个程序（命令），如
//#date;ls -l，单个或多个命令通过cmd传入Job结构体中
typedef struct
{
    char* cmd; //单条命令或多条命令(用分号隔开）
    int progs_num;    //作业中包含程序的数量
    Program* progs;   //各个程序的命令行参数
}Job;

//创建作业
extern Job* create_job(char* cmd);
//销毁作业
extern void destroy_job(Job* job);
//创建进程（命令）
extern Program* create_program(char** arg);
//销毁进程（命令）
extern void destroy_program(Program* prog);
//将命令加入作业中
extern int add_program(Job* job, Program* prog);

#endif

//job.c

#include "job.h"
#include <malloc.h>
#include <assert.h>
#include <string.h>

//创建作业
Job* create_job(char* cmd)
{
    Job* job = (Job*)malloc(sizeof(Job));
    assert( job != NULL);
    
    job->cmd = (char*)malloc(sizeof(char) * strlen(cmd));
    assert(job->cmd != NULL);
    strcpy(job->cmd, cmd);

    job->progs_num = 0;
    job->progs = NULL;

    return job;
}

//销毁作业
void destroy_job(Job* job)
{
    assert(job != NULL);
    free(job->progs);
    free(job->cmd);
    free(job);
}

//arg格式：command  arg0 arg1 ==> 返回3
static int arg_num(char** arg)
{
    int ret = 0;
    char* start = arg[0];
   
    while(start != NULL){
        start = arg[++ret];
    }

    return ret;
}

//创建进程（命令）
Program* create_program(char** arg)
{
    Program* prog = (Program*)malloc(sizeof(Program));
    assert(prog != NULL);
    
    int counter = arg_num(arg);
    prog->args = (char**)calloc(counter + 1, sizeof(char*)); //以NULL结尾

    int i = 0;
    for(i=0; i< counter; i++){
       int len = strlen(arg[i]);
       prog->args[i] = (char*)malloc(len);
       assert(prog->args[i] != NULL);

       strcpy(prog->args[i], arg[i]);
    }

    prog->args[i] = NULL;  //指针数组，以NULL结尾

    return prog;
}

//销毁进程（命令）
void destroy_program(Program* prog)
{
    assert(prog != NULL);

    int i = 0;    
    while(prog->args[i] != NULL)
    {
        free(prog->args[i++]);        
    }

    free(prog->args);
    free(prog);
}

//将命令加入作业中
int add_program(Job* job, Program* prog)
{
    //重新申请一片空间以增加一条命令进来，放入job->progs中
    Program* ps = (Program*)malloc(sizeof(Program) * (job->progs_num + 1));
    memcpy(ps, job->progs, job->progs_num * sizeof(Program));
    
    ps[job->progs_num++] = *prog;//将新的进程（命令）加入进来
    
    free(job->progs); //释放旧的程序（命令）组
    job->progs = ps;

    return job->progs_num - 1; //返回新命令的索引号
}

//mshell.c

#include "job.h"
#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <malloc.h>
#include <string.h>
#include <assert.h>

char* prompt = "mshell> "; //命令行的提示符
#define MAX_COMMAND_LEN 256 //命令行最多的字符数

//cd命令
void cd_fun(Program* prog)
{
    if(chdir(prog->args[1]) < 0){
        perror("cd error");
    }
}

//pwd命令
void pwd_fun(Program* prog)
{
    char buffer[256];
    memset(buffer, 0, sizeof(buffer));

    if(getcwd(buffer, sizeof(buffer)) == NULL){
        perror("pwd error");
    }

    printf("%s\\n", buffer);
}

//分析命令所带的参数（含进程名本身）
void split_cmd(Job* job, char* arguments)
{
    char** args = (char**)malloc(MAX_COMMAND_LEN * sizeof(char*));
    assert( args != NULL);

    char* cmd = strtok(arguments, " ");

    args[0] = (char*)malloc(strlen(cmd) * sizeof(char)); //命令本身
    strcpy(args[0], cmd);

    int i = 1;
    char* s = NULL;
    while((s = strtok(NULL, " ")) != NULL){  //将参数分隔出来
        args[i] = (char*)malloc(strlen(s) * sizeof(char));
        strcpy(args[i++], s);
    }

    //根据args创建一个Program
    Program* prog = create_program(args);
    add_program(job, prog);

    int j = 0;
    for(j=0; j < i; j++){
        free(args[j]);
    }

    free(args);
}

//多条命令的解析
void parse_cmd(Job* job, char* line)
{
    char buff [MAX_COMMAND_LEN];

    //以“;”号分隔多条命令
    char*  pos = line; 
    char*  start = line;
    int count = 0;
    while( start < (line + strlen(line)) ){
        memset(buff, 0, sizeof(buff));
        if((pos = strchr(pos, \';\')) == NULL)
        {
            pos = line + strlen(line);      
        }

        count = pos-start;
        if(count > 0 ){
             memcpy(buff, start, count);
             split_cmd(job, buff);
        }
        start = ++pos;
    }
}

//执行命令
void execute_cmd(Job* job)
{
    int i = 0;
    for(i=0; i<job->progs_num; i++)
    {
        //cd命令
        if(!strcmp(job->progs[i].args[0], "cd")){
           cd_fun(&job->progs[i]);
        }

        //pwd命令
        if(!strcmp(job->progs[i].args[0], "pwd")){
           pwd_fun(&job->progs[i]);
        }

        //quit命令
        if(!strcmp(job->progs[i].args[0], "quit")){
           exit(0);
           return;
        }
    }
}

int main(int argc, char* argv[])
{
    char buffer[MAX_COMMAND_LEN];
    memset(buffer, 0, MAX_COMMAND_LEN);

    ssize_t size = strlen(prompt) * sizeof(char);
    write(STDOUT_FILENO, prompt, size);

    ssize_t len = 0;
    while(1){
        len = read(STDIN_FILENO, buffer, MAX_COMMAND_LEN);
        buffer[len -1] = 0;  //以NULL结尾

        if(strlen(buffer) > 0){
            Job* job = create_job(buffer);
            
            //解析命令
            parse_cmd(job, buffer);
            //执行命令
            execute_cmd(job);

            destroy_job(job);
        }

        write(STDOUT_FILENO, prompt, size);
        memset(buffer, 0, MAX_COMMAND_LEN);
    }

    return 0;
}