How do I merge one directory into another using Bash?

cp -RT source/ destination/

All files and directories in source will end up in destination. For example, source/file1 will be copied to destination/file1.

The -T flag stops source/file1 from being copied to destination/source/file1 instead. (Unfortunately, cp on macOS does not support the -T flag.)

You probably just want cp -R $1/* $2/ — that's a recursive copy.

(If there might be hidden files (those whose names begin with a dot), you should prefix that command with shopt -s dotglob; to be sure they get matched.)

Take a look at rsync

rsync --recursive html/ html_new/

Rsync got alot of flags to set so look at rsync manpage for details

Just use rsync - it's a great tool for local file copy and merging in addition to remote copying.

rsync -av /path/to/source_folder/ /path/to/destination_folder/

Note that the trailing slash on the source folder is necessary to copy only the contents of source_folder to the destination. If you leave it off, it will copy the source_folder and it's contents, which is probably not what you are looking for since you want to merge folders.