In order to install a Magento extension, the first step is usually to add the required files and folders to your current Magento installation. This can be a real pain on a Mac since its merge utility is rudimentary at best.
This is where rsync (which is available from the command line) comes in handy.
-a archive mode
Merge all files and folders from source to destination (will overwrite files, not folders, in destination if source file exist with the same name under the same path)
rsync -arv SOURCE_DIR DEST_DIR
Merge all files and folders from source to destination with the following rules:
- Do not overwrite files which already exist
- Skip destination files that are newer than the source
rsync -arvu SOURCE_DIR DEST_DIR --ignore-existing