#include"apue.h" int userlogin(struct passwd **); int main() {  int ret,i=0;  long ret_cwd;  struct passwd *pw;  char buf[128],hostname[16],usercwd[128];  char *ptmp1;  do{   ret = userlogin(&pw);  }while(ret != 1);  getchar();  while(1){ //to gethostname   if(gethostname(buf,128)!=0){    perror("gethostname()");    return 0;   } //truncate hostname untill '.'   while(buf[i]!='.'){    hostname[i++] = buf[i];   }   i = 0; //if the user is 'root' the symbol is '#' //else '$' //and the current work path is truncated from the last '/' to the end   ret_cwd = (long)getcwd(usercwd,128);   if(strcmp(usercwd,pw->pw_dir)==0){    ret = sprintf(usercwd,"~",NULL);   }   else if(strcmp(usercwd,"/")!=0){    ptmp1 = strrchr(usercwd,'/');    sprintf(usercwd,"%s",ptmp1+1);   }   if(strcmp(pw->pw_name,"root")==0){    sprintf(buf,"*[%s@%s %s]# ",      pw->pw_name,hostname,usercwd);   }   else{    sprintf(buf,"*[%s@%s %s]$ ",      pw->pw_name,hostname,usercwd);   } //command   ssize_t g_ret,len;   char *line = NULL,*s_ret,*ptr=NULL;   int con_cd=0;   fprintf(stderr,"%s",buf);   g_ret = getline(&line,&len,stdin);   line[strlen(line)-1] = '';   if(strcmp(line,"exit")==0){    exit(-1);   }   ptr = line;   s_ret = line;   system(line);   while(ptr!=NULL){    s_ret = (char *)strsep(&ptr," ");    if(strcmp(s_ret,"cd") == 0){     con_cd=1;     continue;    }    else if(con_cd == 1){     chdir(s_ret);    }   }  }  return 0; } //login function int userlogin(struct passwd **pw) {  char name[32],*passwd,*pret;  struct spwd *sp;  printf("login:");  fflush(stdout);  scanf("%s",name);  passwd = getpass("password:");  sp = getspnam(name);  if(sp == NULL){   fprintf(stdout,"no is user![%s]n",name);   return 0;  }  pret = crypt(passwd,sp->sp_pwdp);  if(pret == NULL){   fprintf(stdout,"crypt(%s)n",name);   return 0;  }  if(strcmp(pret,sp->sp_pwdp) == 0){   printf("login successful!n");  }  else{   fprintf(stdout,"passwd is error!n");   return 0;  }  *pw = getpwnam(name);  if(*pw == NULL){   printf("getpwnam(%s) errorn",name);   return 0;  }  return 1; }