Rename using first 5 characters of filename

I would like to create a rule that "simply" renames a file based on the first five characters of the filename. The samples in question look something like
where 28366 represents my file number, the _HUBER_RAIL represent essentially a control, and the rest of it is both the timestamp (before the .) and something unique the app generating the file is creating. My rule will be activated by the presence of _HUBER_RAIL in the name.
Now, I can have these files pretty much named whatever I want to begin with, but because the timestamp and the unique number are out of my control, I'd just as soon leave it as is.
What I need is a way to rename the file just using the first five digits. I've scanned the forum, and see some stuff that kind of addresses this, but gets into custom tokens (which I fiddled with momentarily, and really don't understand) and RegEx stuff (which is over my head at this point).
Can anyone help me understand how I can accomplish this?
Thanks
28366_HUBER_RAIL082520141300.140825010038293.html
where 28366 represents my file number, the _HUBER_RAIL represent essentially a control, and the rest of it is both the timestamp (before the .) and something unique the app generating the file is creating. My rule will be activated by the presence of _HUBER_RAIL in the name.
Now, I can have these files pretty much named whatever I want to begin with, but because the timestamp and the unique number are out of my control, I'd just as soon leave it as is.
What I need is a way to rename the file just using the first five digits. I've scanned the forum, and see some stuff that kind of addresses this, but gets into custom tokens (which I fiddled with momentarily, and really don't understand) and RegEx stuff (which is over my head at this point).
Can anyone help me understand how I can accomplish this?
Thanks