手搓shell

代码

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <ctype.h>
#include <sys/stat.h>
#include <fcntl.h>#define ZERO '\0'
#define SIZE 512
#define SEP " "
#define NUM 32
#define Skiopath(p) do{ p += strlen(p-1);while(*p!='/')p--;}while(0)
#define SkipSpace(cmd,pos) do{while(1){if(isspace(cmd[pos]))pos++;else break;}}while(0)//"ls -a -l -n > myfile.txt"
#define None_Redir 0
#define In_Redir 1
#define Out_Redir 2
#define App_Redir 3int redir_type = None_Redir;
char* filename =NULL;char *gArgv[NUM];
char cwd[SIZE*2];
int lastcode =0;void Die()
{exit(1);
}
const char *Gethome()
{const char *home =getenv("HOME");if(home==NULL)return "/";return home;
}
const char *GetuserName()
{const char *name= getenv("USER");if(name==NULL)return "None";return name;
}
const char *GethostName()
{const char *hostname = getenv("HOSTNAME");if(hostname==NULL)return "None";return hostname;
}
const char *GetCwd()
{const char *cwd=getenv("PWD");if(cwd==NULL)return "None";return cwd;
}
void Makecommandline_print()
{char line[SIZE];const char *username = GetuserName();const char *hostname = GethostName();const char *cwd = GetCwd();Skiopath(cwd);snprintf(line,SIZE,"[%s@%s %s]> ",username,hostname,strlen(cwd)==1?"/":cwd+1);printf("%s",line);fflush(stdout);
}
int Getusercommand(char command[],size_t n)
{char *s = fgets(command,n,stdin);if(s==NULL)return 1;command[strlen(command)-1]=ZERO;return strlen(command);
}void Splitcommand(char command[],size_t n)
{//"ls -a -l -n"-> "ls" "-a" "-l" "-n"gArgv[0] = strtok(command,SEP);int index =1;while((gArgv[index++]=strtok(NULL,SEP)));//done,故意写成=，表示先赋值，在判断。分割之后，strtok会返回NULL，刚好让gArgv最后一个元素是NULL，并且while判断结束}void Executecommand()
{pid_t id =fork();if(id<0) Die();else if(id==0){//重定向设置if(filename != NULL){if(redir_type == In_Redir){int fd =open(filename,O_RDONLY);dup2(fd,0);}else if(redir_type == Out_Redir){int fd =open(filename,O_WRONLY | O_CREAT | O_TRUNC,0666);dup2(fd,1);}else if(redir_type == App_Redir){int fd =open(filename,O_WRONLY | O_CREAT | O_APPEND,0666);dup2(fd,1);}else{}}//childexecvp(gArgv[0],gArgv);exit(errno);}else{//fatherint status =0;pid_t rid = waitpid(id,&status,0);if(rid>0){lastcode = WEXITSTATUS(status);if(lastcode!=0)printf("%s:%s:%d\n",gArgv[0],strerror(lastcode),lastcode);}}}
void Cd()
{const char *path = gArgv[1];if(path==NULL)path=Gethome();//path 一定存在chdir(path);//刷新环境变量char temp[SIZE*2];getcwd(temp,sizeof(temp));//导环境变量snprintf(cwd,sizeof(cwd),"PWD=%s",temp);putenv(cwd);
}
int Checkbuilding()
{int yes =0;const char *enter_cmd = gArgv[0];if(strcmp(enter_cmd,"cd")==0){yes =1;Cd();}else if(strcmp(enter_cmd,"echo")==0&&strcmp(gArgv[1],"$?")==0){yes=1;printf("%d\n",lastcode);lastcode=0;}return yes;
}
void CheckRedir(char cmd[])
{//"ls -a -l -n > myfile.txt"int pos =0;int end=strlen(cmd);while(pos < end){if(cmd[pos] == '>'){if(cmd[pos+1] == '>'){cmd[pos++] = 0;pos++;redir_type = App_Redir;SkipSpace(cmd,pos);filename = cmd +pos;}else{cmd[pos++] = 0;redir_type = Out_Redir;SkipSpace(cmd,pos);filename = cmd +pos;}}else if(cmd[pos] == '<'){cmd[pos++]=0;redir_type = In_Redir;SkipSpace(cmd,pos);filename = cmd+pos;}else {pos++;}}
}
int main()
{int quit =0 ;while(!quit){//0 重置redir_type = None_Redir;filename =NULL;//1.输出一个命令行Makecommandline_print();//2.获取用户命令字符串char usercommand[SIZE];int n = Getusercommand(usercommand,sizeof(usercommand));//2.1 checkredirCheckRedir(usercommand);//3.命令行字符串分割Splitcommand(usercommand,sizeof(usercommand));//4.检查命令是否是内建命令n=Checkbuilding();if(n)continue;//n.执行命令Executecommand();}return 0;
}