Here’s an ‘interactive’ directory merging tool that doesn’t require GUI libraries, printer subsystems, and so forth. It is useful when you want to do things the easy way, at a terminal, without taking your hands off your keyboard. And it works on systems where you don’t have access to install things yourself, such as a shared webhosting server.

echo "#!/bin/bash" > /tmp/mergedir
diff --brief --recursive $1 $2 | awk '/differ/ {print "vimdiff " $2 " " $4 ";"}' >> /tmp/mergedir
chmod +x /tmp/mergedir

Create that as a shell script, chmod +x it, put it in your PATH, and invoke it like this, assuming you called it mergedir:

$ mergedir /some/directory /other/directory

When it finds files that differ, it will open vimdiff on them, and you can use the standard vimdiff commands to merge them (commands such as dp, do, :w, :qa, ]c and so forth – look in the Vim manual for more information).