// 普通 set/get 操作
~~~
$redis->set('test:str1', 'predis');
$ret = $redis->get('test:str1');
echo $ret;
~~~
// setnx 只有在 key 不存在时设置 key 的值
~~~
$redis->setnx('test:str3', 'str3-v');
$ret = $redis->get('test:str3');
echo $ret;
~~~
// incrby/incr/decrby/decr 对值的递增和递减
~~~
$redis->set('test:str2', 1);
$redis->incr('test:str2');
$redis->incrby('test:str2', 4);
echo $redis->decr('test:str2');
echo $redis->decrby('test:str2', 2);
echo $redis->get('test:str2');
~~~
