设置如下：
FILE *f = popen("./output", "r");
int d = fileno(f);
fcntl(d, F_SETFL, O_NONBLOCK);
现在您可以阅读：
ssize_t r = read(d, buf, count);
if (r == -1 && errno == EAGAIN)
no data yet
else if (r > 0)
received data
else
pipe closed
完成后，清理：
pclose(f);
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