进程控制---实现自己的shell
随着第一周的离去,紧随其来的就是第二周的日常了,这一周的任务之一就是实现一个属于自己的shell,好了,让我们来完成它.
首先,附上程序运行的界面,
是不是相当的美观,好了废话不多说,开始实现它.
1.用到的知识点
- 忽视ctrl c终止进程 ; 很简单,一条语句就可以完成,ctrl+c就能强行终止我们的shell的话,那么我们的shell也太弱了点吧.
- readline库和readline函数 : 命令补全,查找历史命令
通过命令来下载库 ,在编译时加上-lreandline就行.
sudo apt-get install libreadline6-dev
ps:博主在安装过程中遇到了冲突,打开更新管理,如下操作即可:
更新完成后,重新下载readline库就好.
使用方法:
- 内置命令cd的实现 : 内建命令cd不能用系统调用来实现,所以需要自己写,也不难,记录下路径名就好.
实现如下 :
- dup()/dup2() : 复制文件描述符
函数原型:
dup:复制参数oldf所指的文件描述符,成功返回最小的相违背使用的文件描述符,失败返回-1.
dup2:同上,可用参数newfd指定新的文件描述符.成功返回文件描述符,失败返回-1.
标准输入的文件描述符 : 0
标准输出的文件描述符 : 1
标准错误输出的文件描述符 : 2
- execvp() : 执行一个可执行程序代替当前程序的映像
函数原型:
execv:以路径名调用可执行文件作为新的进程映像.
execvp:同上,不同之处是:如果参数file包含’/’,那么它作为路径名,若没有’/’,函数则会在PATH环境变量定义的目录中寻找可执行文件.
-
fork() : 创建子进程
函数原型:
fork:该函数有两个返回值,0为子进程返回值,子进程pid为父进程的返回值,创建进程失败返回-1. -
wait() :使父进程暂停,直到它的一个子进程结束为止,返回值为终止运行的pid.
waitpid():使父进程暂停,直到指定子进程结束为止.
函数原型:
2.代码实现
#include
}
void do_cmd(int argcount,char arglist[100][256])
{
int flag = 0; //><| 用于个数的判断
int how = 0; //<>|种类的判断
int background = 0; //&有无的判断
int status;
int pid; //接收fork
int fd; //
int t;
char *arg[argcount+1]; //取出的命令
char *argnext[argcount+1]; //|时用，
char *file;
int i;
for(i=0;i<argcount;i++)
{
arg[i] = (char *)arglist[i];
}
arg[argcount] = NULL;
if(strcmp(arg[0],"ls") == 0)
{
arg[argcount] = "--color=auto";
arg[argcount+1] = NULL;
}
if(strcmp(arg[0],"cd") == 0)
{
getcwd(PATH,100);
if((argcount == 1) || strcmp(arg[1],"~") == 0)
{
strcpy(PATHTEMP,PATH);
strcpy(PATH,"/home");
chdir(PATH);
}
else if(strcmp(arg[1],"-") == 0)
{
chdir(PATHTEMP);
strcpy(PATHTEMP,PATH);
}
else
{
t = chdir(arg[1]);
if(t == -1)
printf("切换目录失败,该目录下没有此文件!\n");
strcpy(PATHTEMP,PATH);
}
return;
}
for(i=0;i<argcount;i++) //判断有无&
{
if(strncmp(arg[i],"&",1) == 0)
{
// printf("aaa\n");
if(i==argcount-1)
{
background = 1;
arg[argcount-1] = NULL;
break;
}
else
{
printf("错误的输入命令！\n");
return;
}
}
}
for(i=0;i<argcount;i++)
{
if(arg[i] != NULL && strcmp(arg[i],">") == 0) //> ---1
{
flag++;
how = 1;
if(arg[i+1] == NULL)
{
flag++;
}
}
if(arg[i] != NULL && strcmp(arg[i],">>") == 0)
{
flag++;
how = 4;
if(arg[i+1] == NULL)
flag++;
}
if(arg[i] != NULL && strcmp(arg[i],"<") == 0) //< ---2
{
flag++;
how = 2;
if(i == 0)
{
flag++;
}
}
if(arg[i] != NULL && strcmp(arg[i],"<<") == 0)
{
flag++;
how = 5;
if(arg[i] == 0)
break;
}
if(arg[i] != NULL && strcmp(arg[i],"|") == 0) //| ---3
{
flag++;
how = 3;
//printf("how = %d\n",how);
if(i == 0 || arg[i+1] == NULL)
{
flag++;
}
}
}
if(flag > 1)
{
printf("wrong command!\n");
return;
}
if(how == 1)
{
for(i=0;arg[i] != NULL;i++)
{
if(strcmp(arg[i],">") == 0)
{
file = arg[i+1]; //?
arg[i] = NULL;
}
}
}
if(how == 4)
{
char name[100];
for(i=0;arg[i] != NULL;i++)
if(strcmp(arg[i],">>") == 0)
{
file = arg[i+1];
arg[i] = NULL;
}
}
if(how == 2)
{
for(i=0;arg[i] != NULL;i++)
{
if(strcmp(arg[i],"<") == 0)
{
file = arg[i+1]; //?
arg[i] = NULL;
}
}
}
if(how == 5)
{
for(i=0;arg[i] != NULL;i++)
if(strcmp(arg[i],"<<") == 0)
{
file = arg[i+1];
arg[i] = NULL;
}
}
if(how == 3)
{
for(i=0;arg[i] != NULL;i++)
{
if(strcmp(arg[i],"|") == 0)
{
arg[i] = NULL;
int j;
for(j=i+1;arg[j] != NULL;j++)
{
argnext[j-i-1] = arg[j];
}
argnext[j-i-1] = NULL;
break;
}
}
}
if((pid = fork()) < 0)
{
printf("fork error!\n");
return;
}
switch(how)
{
case 0:
if(pid == 0)
{
if(!(find_command(arg[0])))
{
printf("%s : command is not found!\n",arg[0]);
exit(0);
}
execvp(arg[0],arg);
exit(0);
}
break;
case 1:
if(pid == 0)
{
if(!(find_command(arg[0])))
{
printf("%s : command is not found!\n",arg[0]);
exit(0);
}
fd = open(file,O_RDWR | O_CREAT |O_TRUNC,0644);
dup2(fd,1);
execvp(arg[0],arg);
exit(0);
}
break;
case 4:
if(pid == 0)
{
if(!(find_command(arg[0])))
{
printf("%s : command is not found!\n",arg[0]);
exit(0);
}
fd = open(file,O_RDWR | O_CREAT | O_APPEND);
dup2(fd,1);
execvp(arg[0],arg);
exit(0);
}
break;
case 2:
if(pid == 0)
{
if(!(find_command(arg[0])))
{
printf("%s : command is not found!\n",arg[0]);
exit(0);
}
fd = open(file,O_RDONLY);
dup2(fd,0);
execvp(arg[0],arg);
exit(0);
}
break;
case 5:
if(pid == 0)
{
if(!(find_command(arg[0])))
{
printf("%s : command is not found!\n",arg[0]);
exit(0);
}
fd = open(file,O_RDONLY);
dup2(fd,0);
execvp(arg[0],arg);
exit(0);
}
break;
case 3:
if(pid == 0)
{
int pid2;
int status2;
int fd2;
if((pid2 = fork()) < 0)
{
printf("fork2 error!\n");
return;
}
else if(pid2 == 0)
{
if(!(find_command(arg[0])))
{
printf("%s : command is not found!\n",arg[0]);
exit(0);
}
fd2 = open("/tmp/my_shell_file",O_WRONLY | O_CREAT | O_TRUNC , 0644);
dup2(fd2,1);
execvp(arg[0],arg);
exit(0);
}
if(waitpid(pid2,&status2,0) == -1)
{
printf("wait for child process error!\n");
}
if(!(find_command(argnext[0])))
{
printf("%s : command is not found!\n",argnext[0]);
exit(0);
}
fd2 = open("/tmp/my_shell_file",O_RDONLY);
dup2(fd2,0);
execvp(argnext[0],argnext);
//getchar();
if(remove("/tmp/my_shell_file"))
printf("remove error!\n");
exit(0);
}
break;
default:
break;
}
if(background == 1) //父进程不等子进程 &
{
printf(" process id : %d \n",pid);
return;
}
if(waitpid(pid,&status,0) == -1)
{
printf("wait for child process error!\n");
}
}
int find_command(char *command)
{
DIR *dp;
struct dirent *dirp;
char *path[] = {"./" , "/bin" , "/usr/bin" , NULL};
if(strncmp(command,"./",2) == 0)
{
command += 2;
}
int i = 0;
while(path[i] != NULL)
{
if((dp = opendir(path[i])) == NULL)
{
printf("can not open /bin !\n");
}
while((dirp = readdir(dp)) != NULL)
{
if(strcmp(dirp->d_name,command) == 0)
{
closedir(dp);
return 1;
}
}
closedir(dp);
i++;
}
return 0;
}
int main()
{
signal(SIGINT, SIG_IGN);
char *buf = NULL; // 录入命令
char arglist[100][256]; //存贮命令
buf = (char *)malloc(256);
if(buf == NULL)
{
perror("malloc error!\n");
exit(-1);
}
// getcwd(PATH,100);
while(1)
{
memset(buf,0,256);
char test[1024] ;
print(test); //提示符
/* char name[100];
gethostname(name,100);
printf("\033[36;1mhello!@%s:\033[0m",name);
getcwd(PATH,100);
printf("\033[34;1m%s$ \033[0m",PATH);
char *str = readline("");
strcpy(buf,str);
add_history(buf);
*/
//getchar();
get_put(buf, test); //录入命令于buf里
//getchar();
// fflush(stdin);
// printf("%s===\n",buf);
if(strcmp(buf,"exit") == 0 || strcmp(buf,"logout") == 0 )
break;
//getchar();
for(int i=0;i<100;i++)
{
arglist[i][0] = '\0';
}
argcount = 0;
//getchar();
explain_input(buf,arglist);//解析命令，存在arglist里
//getchar();
do_cmd(argcount,arglist); //执行命令
}
if(buf != NULL)
{
free(buf);
buf = NULL;
}
return 0;
}