Unlike Windows, copying and moving files in OS X has always been a little confusing. I had previously written about moving/copying files in OS X and those tips still prevail, but there have been some changes to other copy scenarios in OS X Mavericks, mostly when you run into situations where a file or folder name already exists.

In the days of Lion and Mountain Lion, if you copied one folder Test onto another folder Test2, where Test2 contains a folder called Test too, then you could hold down the ALT key and get options to Merge the folders or Keep Both. To be very specific, the button was Merge in Lion and changed to Keep Both in Mountain Lion.

To make it more confusing, now it’s back to Merge in Mavericks, but with a few slight changes. In this article, I’ll walk you through exactly what happens when you copy a folder with the same name to another another that contains a folder with that name.

The best way to learn this is to use an example. I have created a folder called aTestFolder and another folder on the same level called SecondFolder. Inside SecondFolder, I have another folder called aTestFolder.

The first aTestFolder has a file called Test Doc 1 and the second aTestFolder has a file called Test Doc 2. Here’s what it looks like on my system:

folder test mavericks

Now let’s start with a plain and simple copy without pressing any modifier keys. Just drag the aTestFolder onto SecondFolder and you should get a dialog like this:

stop replace os x

The dialog will state:

A newer item named “aTestFolder” already exists in this location. Do you want to replace it with the older one you’re moving?

You can either click Stop or Replace. Stop will cancel and Replace will completely replace the contents of the inner test folder with the contents of the outer test folder. Now let’s do this same thing by pressing and holding down the ALT key and dragging and dropping. You’ll see the following message:

copy merge os x

An item named “aTestFolder” already exists in this location. Do you want to replace it with the one you’re moving? Each folder has unique items such as “aTestFolder” and “Test Doc 2”

Stop will simply cancel everything and Replace All will do the same thing as Replace in the previous example, but now we have the Merge option. Merge will go ahead and join the contents of both the folders, but you only get this option if the content of both folder is unique.

Let me explain. Let’s say I add another file to my inner aTestFolder called Test Doc 1 so that it looks like this now:

merge folder os x

Now go ahead and hold down the ALT key and copy the outer aTestFolder to SecondFolder again. This time you’ll see this message with these options:

stop replace mavericks

Now we are back to getting the same message as in the very first example. This is because there is at least one file or folder inside the two aTestFolders that have the same name. If the data is not unique, you will not get the merge option.

The only way around this is to use the Terminal and commands like cp or rsync. Unfortunately, there is no other way to perform this task in the GUI interface. Most users will never run across this issue, but if you’re a power user on your Mac, you might find this annoying. If you have any questions about copying and merging files in OS X, let us know in the comment. Enjoy!