#include <unistd.h> 
#include <utmp.h>  
#include <stdio.h>  
#include <sys/types.h> 
#include <sys/stat.h> 
#include <time.h>  
#include <fcntl.h> 
#include <string.h>  
     
int get_current_pid(int login_pid); 
char *get_current_procname(int proc_num); 
 
int main(int argc, char **argv) 
{ 
    struct utmp *utmpfp; 
    struct utmp *myutmp; 
 
    char *tty_name = NULL; 
    char *host_ip;  
     
    char now_local_time[50]; 
 
    time_t the_time; 
    struct tm *tm_ptr; 
 
    setutent(); 
 
    // getutent()를 이용해서 utmp정보를 얻어온다. 
    while ((utmpfp = getutent()) != NULL) 
    { 
        // ut_time 은 유닉스 시간으로 저장되는데, localtime 함수를 이용해서 
        // 우리가 쉽게 읽을 수 있는 시간으로 변경했다.     
        the_time = utmpfp->ut_time; 
        tm_ptr = localtime(&the_time); 
        sprintf(now_local_time, "%d/%02d/%02d %02d:%02d", 
                                tm_ptr->tm_year+1900, tm_ptr->tm_mon+1, 
                                tm_ptr->tm_mday, tm_ptr->tm_hour, 
                                tm_ptr->tm_min); 
 
        host_ip = utmpfp->ut_host; 
        if (strlen(host_ip) < 1) 
            host_ip = "-"; 
        if (utmpfp->ut_type == USER_PROCESS) 
        { 
            printf("%-12s %-8s %-12s %s   %s\n", 
                        utmpfp->ut_user,  
                        utmpfp->ut_line, 
                        host_ip, 
                        now_local_time, 
                        get_current_procname(get_current_pid(utmpfp->ut_pid))); 
        } 
    } 
 
 
    return 1; 
} 
 
int get_current_pid(int login_pid) 
{ 
    int  fd; 
    char buf[255]; 
    char stat_file[25]; 
    int  field_num = 7; 
    int  i, j; 
    int  buf_index; 
    char current_pid[11]; 
 
    memset(buf, '\0', 255); 
    sprintf(stat_file, "/proc/%d/stat", login_pid); 
 
    if ((fd = open(stat_file, O_RDONLY)) == -1) 
    { 
        printf("error\n"); 
        return -1; 
    } 
 
    read(fd, buf, 255); 
    j = 0; 
    for (i = 0, buf_index=0; i < 255; i++) 
    { 
        if (buf[i] == ' ') 
        { 
            j++; 
        } 
        else 
        { 
            if (j == field_num) 
            { 
                current_pid[buf_index] = buf[i]; 
                buf_index++; 
            } 
            if (j > field_num) 
                break; 
        } 
    } 
    close(fd); 
    return atoi(current_pid); 
} 
     
char *get_current_procname(int proc_num) 
{    
    char *buf; 
    char proc_file[256]; 
     
    buf = (char *)malloc(256); 
    memset(buf, '\0', 256); 
 
    memset(proc_file, '\0', 256); 
    sprintf(proc_file, "/proc/%d/exe", proc_num); 
 
    readlink(proc_file, buf, 256); 
    return buf; 
} 
 

$ ./myw  
yundream     :0       -            2008/01/17 22:59    
yundream     pts/1    :0           2008/01/17 22:59    
yundream     pts/2    :0           2008/01/17 23:17    
 

# env 
SSH_AGENT_PID=6510 
KDE_MULTIHEAD=false 
MALLOC_CHECK_=2 
SHELL=/bin/bash 
TERM=xterm 
... 
... 
LANG=ko_KR.UTF-8 
GNOME_KEYRING_PID=6453 
KDE_SESSION_UID=1000 
GDM_LANG=ko_KR.UTF-8 
KDEDIRS=/usr/lib/kde4 
GDMSESSION=kde4 
HISTCONTROL=ignoreboth 
SHLVL=2 
 

# echo $LANG 
ko_KR.UTF-8 
 

#include <stdlib.h> 
 
char *getenv(const char *name); 
 

#include <stdlib.h> 
#include <stdio.h> 
 
int main(int argc, char **argv) 
{ 
  char *value = NULL; 
  value = getenv("LANG"); 
  printf("LANG is %s\n", value); 
  return 0; 
} 
 

#include <stdio.h> 
 
int main(int argc, char **argv, char **env) 
{ 
  while(*env != NULL) 
  { 
    printf("%s\n", *env); 
    *env++; 
  } 
} 
 

#include <stdlib.h> 
int setenv(const char *name, const char *value, int overwrite); 
 

#include <unistd.h> 
 
int main() 
{ 
    setenv("TEST", "YUNDREAM", 1); 
    execl("/bin/bash", "bash", NULL); 
} 
 

$ echo $TEST 
 
$ echo $SHLVL 
2 
$ ./setenv 
$ echo $TEST 
YUNDREAM 
$ echo $SHLVL 
3 
$ exit 
exit 
$ echo $TEST 
 
$ echo $SHLVL 
2