[galaxy-dev] How can I populate a data_collection output ?

Hi all, I'm working with data_collection as type of input in xml files. but I use all the datasets of a collection to compute some results that I want to push in a "data_collection" output. I know how take each dataset of a data_collection input with my script, like this : <configfile name="shscript"> ... for $f in $input ... </configfile> where $input is defined by <param name=$input1 type=data_collection collection_type=list... in the top of my xml file. But if my script produce some outputs (number of outputs not defined in advance), how can I populate an output as a data_collection with my shscript and how should I define this output in the xml ? Thanks Julie