It also depends on the source of your character information. For example, our group uses TOS to manage characters in a macro-intensive Excel file. I had to first build a bridge worksheet to copy over values and map them to the character sheet values we are using and then built and API that reads the two arrays and updates or creates the attributes for the character's journal. In theory, the API I built could be adapted to any use where you have one array of sheet attributes and another of the extracted values.
It can be a painstaking process with the sheer number of attributes and, again, depending on your source, you may not be able to capture all of the details or map them nicely to an attribute in the character sheet.
There are a lot of flavors for this API and it really depends on the source of the information, more than anything else. What site or program are you using for character sheets? If you aren't already using a digital sheet in someway, you are probably better off entering the Roll20 data manually, unless you have a large amount of identical items for every sheet.