Using the accepted answer to create an alias
oops = "!f(){ \
git add -A; \
if [ \"$1\" == '' ]; then \
git commit --amend --no-edit; \
else \
git commit --amend \"$@\"; \
fi;\
}; f"
then you can do
git oops
and it will add everything, and amend using the same message
or
git oops -m "new message"
to amend replacing the message