使用popen()

示例1

#include <stdio.h> 
int main(int argc, char *argv[])
{ 
    FILE *fp; 
    char buffer[80]; 

    fp=popen("cat /etc/passwd", "r"); 
    fgets(buffer,sizeof(buffer),fp); 
    printf("%s",buffer); 
    return 0;
}

示例2
读取EC20的GPS坐标

int my_strcmp(char *s1, char *s2, int len)
{
		int i;

		for(i = 0; i < len; i++)
		{
			if(s1[i] != s2[i])
				return 0;
		}
		
		return 1;
}



char *my_strfind(char *buf, char *s, char s_len, int len)
{
		int i,j,tmp;
		//printf("buf %s s %s len %d\n",buf,s,len);
		//printf("slen %d\n", sizeof(s));  

		for(i = 0; i < len; i++)
		{
			tmp = my_strcmp(&buf[i], s, s_len);
			if(tmp == 1)
			{
				//printf("cmp ok\n"); 
				return &buf[i];
			}
		}

		return 0;
}



char *my_strcpy(char *s1, char *s2, char end)
{
	int i;

	for(i = 0; i < 20; i++)
	{
		if(s2[i] == end)
			break;
		s1[i] = s2[i];
	}

	return &s2[i];
}



int gps_get(char *buf, int len, char *longitude, char *latitude)
{
	const char GPS_HEAD[] = "$GPRMC";
	char i = 0,j = 0,*cur;
	int ret = 0;

	cur = my_strfind(buf, (char *)GPS_HEAD, 6, (1024 - sizeof(GPS_HEAD)));
	//printf("cur = %c\n",*cur); 

	if(cur != 0)
	{
		cur = my_strfind(cur, "A,", 2, 60);
		//printf("cur = %c\n",*cur); 
		if(cur != 0)
		{
				//printf("cur = %c\n",*cur);
				cur = my_strcpy(latitude, (cur+2), ',');
				//printf("cur = %c\n",*cur); 
				cur = my_strcpy(longitude, (cur+3), ',');
		}
	}

	return 0;
}

int read_gps(float *lon, float *lat)
{

    static char state = 0,serial_buff[1024] = {0}, lon_tmp[20] = {0}, lat_tmp[20] = {0};
    int ret = 0,Gps_fd = 0;
    float tmp[2];
    FILE *fp;

    if(state == 0)
    {
        system("echo -e \"AT+QGPS=1\r\n\" > /dev/ttyUSB2");//open gps
        state = 1;
    }
    else
    {
        fp=popen("cat /dev/ttyUSB1", "r"); 
        fread(serial_buff, sizeof(char), 1024, fp);
        ret = strlen(serial_buff);
        //printf(serial_buff);

        if(ret > 1)
        {
            ret = gps_get(serial_buff, 1024, lon_tmp, lat_tmp);
            if(ret == 0)
            {
                ret = sscanf(lon_tmp, "%f", &tmp[0]);
                tmp[1] = (unsigned int)(tmp[0]/100);
                tmp[0] = ((tmp[0]/100.0) - tmp[1])*100/60;
                *lon = tmp[0] + tmp[1];

                ret = sscanf(lat_tmp, "%f", &tmp[0]);
                tmp[1] = (unsigned int)(tmp[0]/100);
                tmp[0] = ((tmp[0]/100.0) - tmp[1])*100/60;
                *lat = tmp[0] + tmp[1];
                //printf("\ngps %f %f\n", *lon, *lat);
            }   
        }

        memset(serial_buff, 0, 1024);
        memset(lon_tmp, 0, 20);
        memset(lat_tmp, 0, 20);
    }

    return 0;
}