Makefile: make text file and append strings in it - makefile

Question

I'm having difficulties with makefiles.
So in a recipe, I'm making a file (with a name and a .ujc extension) in a for loop and would like to have a text file at the end which contains all the created files. Purpose is to feed it to an application.
For example, in a semi high-level example,
List= [Class1,Class2,Class3]
foreach(Class C in List) {
#do operations on C > outputs a ClassX.ujc file
# add name of file to a text file named "list_of_files"
}
At the end I should have a text file, list_of_files.txt, which contains the following string:
Class1.ujc Class2.ujc Class3.ujc
As a reference, the code I have at the moment (and which does a bit of the stuff above but does not work is) is:
pc: $(APP)
$(foreach C, $(shell echo $(CLASS) | tr ',' ' '), \
make -C BUILDENV CLASS=$(C) BUILD=just_filelist OUTPUT=filelist.txt SKIPSELF=yes && \
../classCvt/classCvt <./Applications/$(C).class> ./Applications/$(C).ujc && \
cat app_file_list.txt | xargs echo ./Applications/$(C).ujc >app_file_list.txt && \
) true
time -p ./$(APP) `cat app_file_list.txt` `cat filelist.txt`
The internal make does make a filelist which is fed to the app, but I'd also like to feed the app_file_list but its construction goes totally wrong.
Probably simple, but I'm not getting there.
Edit:
The code below does what I want:
pc: $(APP)
rm -f cat app_file_list.txt
$(foreach C, $(shell echo $(CLASS) | tr ',' ' '), \
make -C BUILDENV CLASS=$(C) BUILD=just_filelist OUTPUT=filelist.txt SKIPSELF=yes && \
../classCvt/classCvt <./Applications/$(C).class> ./Applications/$(C).ujc && \
cat app_file_list.txt | echo ./Applications/$(C).ujc >>app_file_list.txt && \
) true
time -p ./$(APP) `cat app_file_list.txt` `cat filelist.txt`
Notable mistake I made was the xargs.

Answer 1

(Also in the post)
The solution turned out to be not-so-difficult. I needed to remove the xargs command and do the correct operation (i.e., >> instead of >) in the 'cat app_file_list.txt | etc...' line.
The code below does what I want:
pc: $(APP)
rm -f cat app_file_list.txt
$(foreach C, $(shell echo $(CLASS) | tr ',' ' '), \
make -C BUILDENV CLASS=$(C) BUILD=just_filelist OUTPUT=filelist.txt SKIPSELF=yes && \
../classCvt/classCvt <./Applications/$(C).class> ./Applications/$(C).ujc && \
cat app_file_list.txt | echo ./Applications/$(C).ujc >>app_file_list.txt && \
) true
time -p ./$(APP) `cat app_file_list.txt` `cat filelist.txt`
Notable mistake I made was the xargs which caused strings to repeat into the .txt file.