c 语言中调用unix 命令

#include <stdio.h>#include <stdlib.h>int main(int argc, char **argv){FILE *fp = NULL;char buff[1000] = {0};char rsl[20] ={0};int iRsl = 0;strcpy(buff, "ps -ef | grep oweqry_server | grep -v grpe | wc -l");if ((fp = popen(buff, "r")) != NULL){        fgets(rsl, 100, fp) ;        pclose(fp);}iRsl = atoi(rsl);printf("rsl:[%s], [%d]\n", rsl, iRsl);return 0;}