注意： 本文章只是为了理解shell内部的工作原理， 所以并没有完成shell的所有工作， 只是完成了shell里的一小部分工作

#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <assert.h>
#include <sys/types.h> 
#include <sys/wait.h>#define LEFT "["
#define RIGHT "]"
#define END "#"
#define SPLIT " "
#define LINE_SIZE 1024
#define ARGV_SIZE 32
#define EXIT_CODE 66
#define PWD_SIZE 100int lastexit = 0;
int quit = 0;
char pwd[PWD_SIZE];const char* getusername() {return getenv("USER");
}const char* mygethostname() {return getenv("HOSTNAME");
}void getpwd() {getcwd(pwd, PWD_SIZE);
}void display() {getpwd();printf(LEFT"%s@%s %s"RIGHT""END" ", getusername(), mygethostname(), pwd);
}void getinput(char* cline, int size) {char* s = fgets(cline, size, stdin);assert(s != NULL);cline[strlen(cline) - 1] = '\0';//printf("%s\n", cline);
}int split(char* cline, char* argv[]) {int i = 0;//printf("%s", cline);argv[i ++] = strtok(cline, SPLIT);while (argv[i ++] = strtok(NULL, SPLIT));return i - 1;
}void normalExe(char* argv[]) {extern char** environ;pid_t id = fork();if (id < 0) {perror("fork");//continue;} else if (id == 0) {// childexecvpe(argv[0], argv, environ);exit(EXIT_CODE);}// fatherint status = 0;pid_t ret = waitpid(id, &status, 0);//  if (ret > 0) printf("wait success pid: %d\n", ret);if (ret > 0) lastexit = WEXITSTATUS(status);
}int neijian(char* argv[], int argc) {if (argc == 2 && strcmp(argv[0], "cd") == 0) {chdir(argv[1]);getpwd();return 1;}return 0;
}int main() {//int quit = 0;char cline[LINE_SIZE];char* argv[ARGV_SIZE] = { NULL };extern char** environ;while (!quit) {display();getinput(cline, LINE_SIZE);int tt = split(cline, argv);if (tt == 0) continue;//printf("%d\n", tt);/*int i = 0;for (i = 0; argv[i]; ++ i)printf("%s ", argv[i]);printf("\n");*/// 内建命令执行//内建命令本质上就是shell内部的一个函数int n = neijian(argv, tt);//printf("%d\n", n); //普通命令执行if (!n) normalExe(argv);}return 0;
}