#include <unistd.h>
#include <stdio.h>
#include <dirent.h>
#include <string.h>
#include <sys/stat.h>
#include <stdlib.h>
 
void printdir(char *dir,int depth){
  DIR *dp;
  struct dirent *entry;
  struct stat statbuf;
 
  if((dp = opendir(dir)) == NULL){
    fprintf(stderr, "cannot open directory: %s\n", dir);
    return;
  }
 
  chdir(dir);
  while((entry = readdir(dp)) != NULL){
    lstat(entry->d_name,&statbuf);
    if(S_ISDIR(statbuf.st_mode)){
      /*Found a directory,but ignore . and ..*/
      if(strcmp(".",entry->d_name) == 0 || strcmp("..",entry->d_name) == 0){
        continue;
      }
      printf("%*s%s/ \n",depth,"",entry->d_name);
      /*Recurse at a new indent level*/
      printdir(entry->d_name,depth+4);
    }else{
      printf("%*s%s \n",depth,"",entry->d_name);
    }
 
  }
}
int main(){
  /*
  show directory
  */
  printf("Directory scan of /home:\n");
  printdir("/home",0);
  printf("done. \n");
   
  exit(0);
}

#include <unistd.h>
#include <stdio.h>
#include <dirent.h>
#include <string.h>
#include <sys/stat.h>
#include <stdlib.h>
 
void printdir(char *dir,int depth){
  DIR *dp;
  struct dirent *entry;
  struct stat statbuf;
 
  if((dp = opendir(dir)) == NULL){
    fprintf(stderr, "cannot open directory: %s\n", dir);
    return;
  }
 
  chdir(dir);
  while((entry = readdir(dp)) != NULL){
    lstat(entry->d_name,&statbuf);
    if(S_ISDIR(statbuf.st_mode)){
      /*Found a directory,but ignore . and ..*/
      if(strcmp(".",entry->d_name) == 0 || strcmp("..",entry->d_name) == 0){
        continue;
      }
      printf("%*s%s/ \n",depth,"",entry->d_name);
      /*Recurse at a new indent level*/
      printdir(entry->d_name,depth+4);
    }else{
      printf("%*s%s \n",depth,"",entry->d_name);
    }
 
  }
}
int main(int argc, char* argv[]){
  /*
  show directory
  */
  char *topdir = ".";
  if(argc >= 2){
    topdir = argv[1];
  }
  printf("Directory scan of %s:\n",topdir);
  printdir(topdir,0);
  printf("done. \n");
   
  exit(0);
}

#include <sys/types.h>
#include <pwd.h>
#include <stdio.h>
#include <unistd.h>
 
int main(){
  uid_t uid;
  gid_t gid;
 
  struct passwd *pw;
  uid = getuid();
  gid = getgid();
 
  printf("User is %s\n",getlogin());
 
  printf("User IDs: uid=%d, gid=%d \n", uid, gid);
 
  pw = getpwuid(uid);
  printf("UID passwd entry: \n name=%s, uid=%d, gid=%d, home=%s, shell=%s\n",pw->pw_name, pw->pw_uid, pw->pw_gid, pw->pw_dir, pw->pw_shell);
 
  pw = getpwnam("root");
  printf("root passwd entry: \n");
  printf("name=%s, uid=%d, gid=%d, home=%s, shell=%s \n",pw->pw_name, pw->pw_uid, pw->pw_gid, pw->pw_dir, pw->pw_shell);
  exit(0);
}

#include <sys/utsname.h>
#include <unistd.h>
#include <stdio.h>
 
 
int main(){
  char computer[256];
  struct utsname uts;
  if(gethostname(computer, 255) != 0 || uname(&uts) < 0){
    fprintf(stderr, "Could not get host information \n");
    exit(1);
  }
 
  printf("Computer host name is %s \n",computer);
  printf("System is %s on %s hardware \n",uts.sysname, uts.machine);
  printf("Nodename is %s \n",uts.nodename);
  printf("Version is %s , %s \n",uts.release, uts.version);
 
  exit(0);
}