#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 eth100eth100: NO FOUNDif_status = 0# # ifconfig eth0 down# ./netlink eth0 eth0: DOWNif_status = 1# # ifconfig eth0 up# ./netlink eth0eth0: UNPLUGGEDif_status = 2## ./netlink eth0eth0: LINKEDif_status = 3