Before you have asked about starting GUI synchronization from commandline.
Now you ask about "Keep remote directory up to date" in scripting console.
Those are very different features.
For the latter, you can do:

See https://winscp.net/eng/docs/commandline

Really?

https://winscp.net/eng/docs/scriptcommand_keepuptodate
Can I use keepuptodate with -filemask? In the manual it seems possible.

Maybe something like this:

I have not tested it now

There's no command-line -filemask switch.
There's only /rawtransfersettings:

Though that by default changes the file mask permanently. You can prevent that using:

(see https://winscp.net/eng/docs/config#readonly_sections)

Hi,
I want to make a shortcut-link on the Desktop.

'SessName' is the name of a session. There are both paths stored, HD- and server-path. I want to sync all CSV on HD to a path on the server-path and i try this:

In the HD-path are a lot of files, but I want to sync only the spzified files in filemask.

Unfortunately, the filemask-parameter does not provide any restriction, because all file-types are transferred anyway. :-(