#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <ctype.h>

#define TMP_FILE         "/tmp/.ifconfig.log"

int main(int argc, char **argv)
{
        pid_t          pid;
        int            fd;
        char           buf[1024];
        int            rv;
        char          *ptr;
        FILE          *fp;
        char          *ip_start;
        char          *ip_end;
        char           ipaddr[16];

        if( (fd=open(TMP_FILE, O_RDWR|O_CREAT|O_TRUNC, 0644)) < 0 )
        {
                printf("Redirect standard output to file failure: %s\n", strerror(errno));
                return -1;
        }

        pid = fork();
        if(pid < 0)
        {
                printf("fork() create child process failure: %s\n", strerror(errno));
                return -1;
        }
        else if( pid == 0 )
        {
                printf("Child process start excute ifconfig program\n");
                dup2(fd, STDOUT_FILENO);
                execl("/sbin/ifconfig", "ifconfig", "eth0", NULL);
                printf("Child process start excute ifconfig program over\n");
                return 0;
        }
         else 
        {
                sleep(3);
        }

        memset(buf, 0, sizeof(buf));

        rv=read(fd, buf, sizeof(buf));
        printf("Read %d bytes data dierectly read after child process write\n", rv);

        lseek(fd, 0, SEEK_SET);
        rv=read(fd, buf, sizeof(buf));
        printf("Read %d bytes data after lseek:\n %s\n ", rv, buf);

        fp = fdopen(fd, "r");
        fseek(fp, 0, SEEK_SET);

        memset(buf, 0, sizeof(buf));

        rv=read(fd, buf, sizeof(buf));
        printf("Read %d bytes data dierectly read after child process write\n", rv);                                                                                    
        printf("Read %d bytes data dierectly read after child process write\n", rv);

        lseek(fd, 0, SEEK_SET);
        rv=read(fd, buf, sizeof(buf));
        printf("Read %d bytes data after lseek:\n %s\n ", rv, buf);

        fp = fdopen(fd, "r");
        fseek(fp, 0, SEEK_SET);

        while( fgets(buf, sizeof(buf), fp) )
        {
                if( strstr(buf, "netmask") )
                {
                        ptr=strstr(buf, "inet");
                        if( !ptr )
                        {
                                break;
                        }
                        ptr += strlen("inet");

                        while( isblank(*ptr) )
                                ptr++;

                        ip_start = ptr;

                        while( !isblank(*ptr) )
                                ptr++;

                        ip_end = ptr;

                        memset(ipaddr, 0, sizeof(ipaddr));
                        memcpy(ipaddr, ip_start, ip_end-ip_start);

                        break;
                }
        }

        printf("Parser and get IP address: %s\n", ipaddr);

        fclose(fp);

        unlink(TMP_FILE);

        return 0;
}