./emqx_ctl data export命令不生效

File: [/zh_CN/advanced/data-import-and-export.md](https://docs.emqx.cn/broker/v4.3/advanced/data-import-and-export.html)

我想在已经启动的实例中导出数据，但是我输入这行命令后并没有按照预期地将数据保存成json文件，而是提醒我emqx_ctl的用法
[xxxx@xxxxx bin]$ ./emqx_ctl export
Usage: emqx_ctl
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mgmt list # List Applications
mgmt insert # Add Application of REST API
mgmt update # Update Application of REST API
mgmt lookup # Get Application of REST API
mgmt delete # Delete Application of REST API
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