#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
 
int get_if_status(char *if_name)
{
  char  buffer[BUFSIZ];
 char  cmd[100];
  FILE  *read_fp;
  int    chars_read;
  int    ret =0;
  
  memset( buffer, 0, BUFSIZ );
  memset( cmd, 0, 100 );
 sprintf(cmd, "ifconfig -a | grep %s",if_name);
  read_fp = popen(cmd, "r");
  if ( read_fp != NULL )
  {
    chars_read = fread(buffer, sizeof(char), BUFSIZ-1, read_fp);
 pclose(read_fp);
 
    if (chars_read > 0)
    {
      ret = 1;
    }
    else
    {
  fprintf(stderr, "%s: NO FOUND\r\n",if_name);
  return 0;
    }
  }
 
 if(ret == 1)
 {
 memset( buffer, 0, BUFSIZ );
 memset( cmd, 0, 100 );
 sprintf(cmd, "ifconfig |grep %s",if_name);
 read_fp = popen(cmd, "r");
 if ( read_fp != NULL )
 {
   chars_read = fread(buffer, sizeof(char), BUFSIZ-1, read_fp);
   pclose(read_fp);
  
   if (chars_read > 0)
   {
     ret = 2;
   }
   else
   {
  fprintf(stderr, "%s: DOWN\r\n",if_name);
  return 1;
   }
 }
 }
 
 if(ret == 2)
 {
 memset( buffer, 0, BUFSIZ );
 memset( cmd, 0, 100 );
 sprintf(cmd, "ifconfig %s | grep RUNNING | awk '{print $3}'",if_name);
 read_fp = popen(cmd, "r");
 if ( read_fp != NULL )
 {
   chars_read = fread(buffer, sizeof(char), BUFSIZ-1, read_fp);
   pclose(read_fp);
  
   if (chars_read > 0)
   {
  fprintf(stderr, "%s: LINKED\r\n",if_name);
  return 3;
   }
   else
   {
  fprintf(stderr, "%s: UNPLUGGED\r\n",if_name);
  return 2;
   }
 }
 }
 
 return -1;
}
 
 
int main(int argc, char* argv[])
{
  int i=0;
 if(argc != 2)
 {
 fprintf(stderr, "usage: %s <ethname>", argv[0]);
 return -1;
 }
 
  i = get_if_status(argv[1]);
  printf( "if_status = %d\n", i );
  return 0;
}

# ./netlink eth100
eth100: NO FOUND
if_status = 0
# 
# ifconfig eth0 down
# ./netlink eth0 
eth0: DOWN
if_status = 1
# 
# ifconfig eth0 up
# ./netlink eth0
eth0: UNPLUGGED
if_status = 2
#
# ./netlink eth0
eth0: LINKED
if_status = 3