You could use unoconv to transform the Calc sheet into csv. But unoconv seems to be quite instable, i didn't manage to get it working on a simple ods (calc) file.

A better choice is jodconverter. It's available in universe, so you can install it using apt. Jodconverter requires an instance of openoffice running and listening on port 8100.

To "manually" convert this sheet

from ods to csv:

$ soffice -headless -accept="socket,port=8100;urp;"

$ jodconverter Untitled1.ods Untitled1.csv

The resulting csv will look like this:

$ cat Untitled1.csv 

"A","B","C","D"

34,68,23,3

34234,68468,34,1

3423,6846,34,34535

If you don't need the table structure but just the contents for indexing purposes, take a look at odt2txt. It seems to be able to handle ods files, too, but it won't preserve the table structure. It doesn't require q soffice process running. With the sheet shown above, you will receive the following output:

$ odt2txt Untitled1.ods 



A



B



C



D



34



23



3



34234



3



34



1



3423



234



34



34535