引言
在暑假留校的第二周,我们的项目是学习进程并切实现自己的shell;关于什么是shell请大家自行百度,简单来说shell就是指一个面向用户的命令接口，表现形式就是一个可以由用户录入的界面，这个界面也可以反馈运行信息;
不是目录的目录
- 项目需求
- 如何实现
- 源代码
1.项目需求
关于进阶需求我们只讲述管道的实现,对与后面三个,全部都是调用readline这个库我们不做概述
2.1有一个好看的shell界面
//打印提示符
void print_prompt()
{
struct passwd *usrname;
usrname = getpwuid(getuid());
char buf[256];
memset(buf,0,sizeof(buf));
printf("my_shell:%s",getcwd(buf,256));
if(strcmp(usrname->pw_name,"root")==0)
printf("#");
else
printf("$");
}
我们为了和终端真实的界面差不多,所以在这里花费了一些心思;
首先是通过getcwd()获得了当前所在目录;
然后通过getpwuid(getuid())获得了当前的实际用户是root还是一般用户;
2.２内建命令cd的实现
这是我实现的第一个需求,因为内建命令不需要开进程,所以我选择先实现cd命令,实现了进阶功能cd -;
关于cd -的实现本来我想使用队列来解决,但是其实只有两个数据,所以我采用了if - else来进行简单实现;
struct dd{
char haha[2][256];
int ha;
}cd;
//内置命令直接执行
void in_cd(char list[100][256],int cont)
{
if(strcmp(list[0],"cd") != 0)
return;
char buf[256];
struct passwd *usrname;
usrname = getpwuid(getuid());
getcwd(cd.haha[cd.ha],sizeof(cd.haha[cd.ha]));
if(cd.ha == 0)
cd.ha++;
else
cd.ha--;
if(strcmp(list[1],"~")==0)
{
if(strcmp(usrname->pw_name,"xzwb")==0)
strcpy(buf,"/home/xzwb/");
else if(strcmp(usrname->pw_name,"root")==0)
strcpy(buf,"/root/");
}
else if(strcmp(list[1],"-")==0)
strcpy(buf,cd.haha[cd.ha]);
else
strcpy(buf,list[1]);
chdir(buf);
}
上面就是cd命令的实现;
2.3重定向和管道和后台运行部分的实现
- 关于重定向的实现相对来说也挺简单的,就是判断你是不是重定向然后找到你重定向的文件,通过
dup2()这个函数可以将重定向文件的文件描述符修改为0,1来实现输入输出重定向; - 关于管道的实现就是先开一个进程执行管道的前一部分,存入文件中,然后再开一个进程执行后一部分将前一部分文件中的东西,使用
dup2修改为标准输入; - 后台运行命令是我觉得最简单的一部分,就是主进程要不要阻塞住等待子进程执行完毕;
//实现除了cd以外的外部命令
void in_command(char list[100][256] , int cont)
{
int background = 0; //标识是否有后台运行符&
int how = 0; //用于标识是否有><|
pid_t pid;
int i;
int fd;
int he;
int statu;
char *arg[256];
char *arg2[256];
char *file;
for(i=0;i<cont;i++)
arg[i] = (char*)list[i];
arg[cont] = NULL;
for(i=0;i<cont;i++)
{
if(strcmp(arg[i],">")==0)
{
file = arg[i+1];
how += 1;
he = i;
}
if(strcmp(arg[i],"<")==0)
{
file = arg[i+1];
how += 2;
he = i;
}
if(strcmp(arg[i],">>")==0)
{
file = arg[i+1];
how += 11;
he = i;
}
if(strcmp(arg[i],"<<")==0)
{
file = arg[i+1];
how += 22;
he = i;
}
if(strcmp(arg[i],"|")==0)
{
int c = 0;
for(int j = i+1 ; j < cont;j++,c++)
arg2[c] = arg[j];
arg2[c] = NULL;
how += 4;
he = i;
}
if(strcmp(arg[i],"&")==0)
{
arg[i] = NULL;
background += 1;
}
}
if(how!=0)
arg[he] = NULL;
if(background == 1 && strcmp(list[cont-1],"&") != 0)
background--;
if((pid = fork())<0)
perror("fork error\n");
if(pid == 0)
{
switch(how)
{
case 0:
{
execvp(arg[0],arg);
exit(0);
break;
}
case 1:
{
fd = open(file,O_RDWR|O_CREAT|O_TRUNC,S_IRWXU);
dup2(fd,1);
execvp(arg[0],arg);
exit(0);
break;
}
case 2:
{
if((fd = open(file,O_RDONLY,0644)) < 0)
printf("openfile falsh\n");
close(0);
dup2(fd,0);
execvp(arg[0],arg);
exit(0);
break;
}
case 11:
{
fd = open(file,O_RDWR|O_CREAT|O_APPEND,S_IRWXU);
dup2(fd,1);
execvp(arg[0],arg);
exit(0);
break;
}
case 22:
{
if((fd = open(file,O_RDONLY)) < 0)
perror("open");
dup2(fd,0);
execvp(arg[0],arg);
exit(0);
break;
}
case 4:
{
int pid2;
int satu;
int fd2;
if((pid2 = fork()) < 0)
perror("fork error");
if(pid2 == 0)
{
if((fd2 = open("/tmp/1.txt",O_WRONLY|O_CREAT|O_TRUNC,0644)) < 0)
perror("open");
dup2(fd2,1);
execvp(arg[0],arg);
exit(0);
}
waitpid(pid2,&satu,0);
close(fd2);
fd2 = open("/tmp/1.txt",O_RDONLY);
dup2(fd2,0);
execvp(arg2[0],arg2);
if(remove("/tmp/1.txt") < 0)
perror("remove error");
exit(0);
break;
}
default:printf("输入错误!\n");
}
}
if(background == 1)
return;
if(background == 0)
waitpid(pid,&statu,0);
}
static void mask_ctrl_c(int signo)
{
printf("\n");
print_prompt();
fflush(stdout);
}
3.源代码
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <fcntl.h>
#include <dirent.h>
#include <sys/stat.h>
#include <pwd.h>
#include <signal.h>
#include <readline/readline.h>
#include <readline/history.h>
struct dd{
char haha[2][256];
int ha;
}cd;
struct history{
char a[100];
struct history *next;
};
//打印提示符
void print_prompt()
{
struct passwd *usrname;
usrname = getpwuid(getuid());
char buf[256];
memset(buf,0,sizeof(buf));
printf("my_shell:%s",getcwd(buf,256));
if(strcmp(usrname->pw_name,"root")==0)
printf("#");
else
printf("$");
}
//获得命令行输入
void get_input(char *buf)
{
int len = 0;
char ch;
ch = getchar();
while(len < 256 && ch != '\n')
{
buf[len++] = ch;
ch = getchar();
}
if(len == 256)
{
printf("command is too long\n");
exit(1);
}
buf[len] = '\n';
buf[++len] = '\0';
}
//解析命令行
void explain_input(char *buf , int *cont , char list[100][256])
{
int i=0;
*cont = 0;
int j;
while(1)
{
if(buf[i] == ' ')
{
i++;
continue;
}
if(buf[i] == '\n')
break;
else
{
j = 0;
while(buf[i] != ' ' && buf[i] != '\n')
{
list[*cont][j] = buf[i];
j++;
i++;
}
list[*cont][j] = '\0';
*cont += 1;
}
}
}
//内置命令直接执行
void in_cd(char list[100][256],int cont)
{
if(strcmp(list[0],"cd") != 0)
return;
char buf[256];
struct passwd *usrname;
usrname = getpwuid(getuid());
getcwd(cd.haha[cd.ha],sizeof(cd.haha[cd.ha]));
if(cd.ha == 0)
cd.ha++;
else
cd.ha--;
if(strcmp(list[1],"~")==0)
{
if(strcmp(usrname->pw_name,"xzwb")==0)
strcpy(buf,"/home/xzwb/");
else if(strcmp(usrname->pw_name,"root")==0)
strcpy(buf,"/root/");
}
else if(strcmp(list[1],"-")==0)
strcpy(buf,cd.haha[cd.ha]);
else
strcpy(buf,list[1]);
chdir(buf);
}
//实现除了cd以外的外部命令
void in_command(char list[100][256] , int cont)
{
int background = 0; //标识是否有后台运行符&
int how = 0; //用于标识是否有><|
pid_t pid;
int i;
int fd;
int he;
int statu;
char *arg[256];
char *arg2[256];
char *file;
for(i=0;i<cont;i++)
arg[i] = (char*)list[i];
arg[cont] = NULL;
for(i=0;i<cont;i++)
{
if(strcmp(arg[i],">")==0)
{
file = arg[i+1];
how += 1;
he = i;
}
if(strcmp(arg[i],"<")==0)
{
file = arg[i+1];
how += 2;
he = i;
}
if(strcmp(arg[i],">>")==0)
{
file = arg[i+1];
how += 11;
he = i;
}
if(strcmp(arg[i],"<<")==0)
{
file = arg[i+1];
how += 22;
he = i;
}
if(strcmp(arg[i],"|")==0)
{
int c = 0;
for(int j = i+1 ; j < cont;j++,c++)
arg2[c] = arg[j];
arg2[c] = NULL;
how += 4;
he = i;
}
if(strcmp(arg[i],"&")==0)
{
arg[i] = NULL;
background += 1;
}
}
if(how!=0)
arg[he] = NULL;
if(background == 1 && strcmp(list[cont-1],"&") != 0)
background--;
if((pid = fork())<0)
perror("fork error\n");
if(pid == 0)
{
switch(how)
{
case 0:
{
execvp(arg[0],arg);
exit(0);
break;
}
case 1:
{
fd = open(file,O_RDWR|O_CREAT|O_TRUNC,S_IRWXU);
dup2(fd,1);
execvp(arg[0],arg);
exit(0);
break;
}
case 2:
{
if((fd = open(file,O_RDONLY,0644)) < 0)
printf("openfile falsh\n");
close(0);
dup2(fd,0);
execvp(arg[0],arg);
exit(0);
break;
}
case 11:
{
fd = open(file,O_RDWR|O_CREAT|O_APPEND,S_IRWXU);
dup2(fd,1);
execvp(arg[0],arg);
exit(0);
break;
}
case 22:
{
if((fd = open(file,O_RDONLY)) < 0)
perror("open");
dup2(fd,0);
execvp(arg[0],arg);
exit(0);
break;
}
case 4:
{
int pid2;
int satu;
int fd2;
if((pid2 = fork()) < 0)
perror("fork error");
if(pid2 == 0)
{
if((fd2 = open("/tmp/1.txt",O_WRONLY|O_CREAT|O_TRUNC,0644)) < 0)
perror("open");
dup2(fd2,1);
execvp(arg[0],arg);
exit(0);
}
waitpid(pid2,&satu,0);
close(fd2);
fd2 = open("/tmp/1.txt",O_RDONLY);
dup2(fd2,0);
execvp(arg2[0],arg2);
if(remove("/tmp/1.txt") < 0)
perror("remove error");
exit(0);
break;
}
default:printf("输入错误!\n");
}
}
if(background == 1)
return;
if(background == 0)
waitpid(pid,&statu,0);
}
static void mask_ctrl_c(int signo)
{
printf("\n");
print_prompt();
fflush(stdout);
}
void history_ai(char list[100][256])
{
if(strcmp(list[0],"history")==0)
{
read_history(NULL);
}
}
int main()
{
cd.ha = 0;
int cont;
int len;
char list[100][256];
signal(SIGINT,mask_ctrl_c);
while(1)
{
char *buf = (char*)malloc(sizeof(256));
memset(list,0,sizeof(list));
memset(buf,0,sizeof(buf));
print_prompt();
buf = readline("myshell&");
add_history(buf);
write_history(NULL);
buf[strlen(buf)] = '\n';
if(strcmp(buf,"exit\n") == 0)
exit(0);
explain_input(buf,&cont,list);
in_cd(list,cont);
history_ai(list);
in_command(list,cont);
free(buf);
}
}