Description
Increment the number stored at key by one. If the second argument is filled, it will be used as the integer value of the increment.
对指定的KEY的值自增1。如何填写了第二个参数，将把第二个参数自增给KEY的值。
Parameters
key
value: value that will be added to key (only for incrBy)
Return value
INT the new value
返回新的INT数值
Examples
$redis->incr('key1'); /* key1 didn't exists, set to 0 before the increment 如果key1不存在，在自增之前的默认值为0 */
/* and now has the value 1 执行incr后，现在为1 */
$redis->incr('key1'); /* 2 */
$redis->incr('key1'); /* 3 */
