It turns out that we can use LibreOffice to mass convert OpenDocument, such as odf, ods, or etc, to other format. What I need is to mass convert ods files to xls. We just need a single line to convert a file.
For example, when we want to convert file.ods to file.xls on current folder, we use the following line in bash:
To mass convert all file in current folder, use the following code:
soffice --headless --convert-to xls file.ods
Sample code can be found in https://github.com/joielechong/collection_of_script under bash folder.
for i in *.ods; do soffice --headless --convert-to xls "$i" ; done