.cpp-->.txt
find ./ -name "*.cpp" | awk -F "." '{print $2}' | xargs -i -t mv ./{}.cpp ./{}.txt
.txt-->.cpp
find ./ -name "*.txt" | awk -F "." '{print $2}' | xargs -i -t mv ./{}.txt ./{}.cpp

.h-->.txt
find ./ -name "*.h" | awk -F "." '{print $2}' | xargs -i -t mv ./{}.h ./{}.txt
.txt-->.h
find ./ -name "*.txt" | awk -F "." '{print $2}' | xargs -i -t mv ./{}.txt ./{}.h

js-->.txt
find ./ -name "*.js" | awk -F "." '{print $2}' | xargs -i -t mv ./{}.js ./{}.txt
txt-->js
find ./ -name "*.txt" | awk -F "." '{print $2}' | xargs -i -t mv ./{}.txt ./{}.js