Write metadata to a single file

[Endowpea]

I use postprocessors can create metadata one file per post,

                    {
                        "name": "metadata",
                        "event": "post",
                        "filename": "{id}.txt",
                        "mode": "custom",
                        "format": "{content}\n\n"
                    }
                  ]

but there ary too many small files
then I add "open": "a" in it, but when I download posts, it will add duplicate metadata, I don't want to do this.
I found -j/--dump-json can print all json, but I don't know how to save it in a file.
I want to write all posts' metadata to a single file, how can I do?

[allendema]

To only use one file:

Filename must remain the same for every file/post. So:

• Use "filename": "{extractor}_metadata.txt".

• Use "open": "a" to append to that .txt file.