Bash script - if a file exists in another directory

I'm new to bash and would like your help; couldn't find an answer for this case. I'm trying to check if the files in one directory exist in another directory

Let's say I have the path /home/public/folder/ (here I have several files) and I want to check if the files exist in /home/private/folder2

I tried that

for file in $firstPath/*
do
   if [ -f $file ]; then
   (ask if to over write etc.. rest of the code) 

And also

for file in $firstPath/*
do
   if [ -f $file/$secondPath ]; then
   (ask if to over write etc.. rest of the code) 

Both don't work; it seems that in the first case, it compares the files in the first path (so it always ask me if I want to overwrite although it doesn't exist in the second path) And in the second case, it doesn't go inside the if statement. How could I fix that?