The Invisible Bit

Tuesday, 15 April 2008

I helped a friend today with a seemingly baffling problem: he could see the files and folders on his desktop (i.e. the icons you see when all windows are closed or hidden), but he couldn’t see the “Desktop” folder itself in his home folder. Ends up, somehow, the folder had been made invisible.

There are a two supported ways¹ to mark files as “invisible” on the Mac:

• Start the file or folder name with a dot (e.g. “.like_this”). This is a Unix convention.
• Toggle the HFS+ invisible bit for the file or folder. This is the Mac convention.

The invisible bit is metadata. In the same way that every file and folder has metadata such as created and modified dates, it has a boolean “invisible” bit. Files marked invisible are still readable and writable, they just don’t show up in the Finder or in Open and Save dialogs. Invisibility is not inherited by the contents of an invisible folder, which explains why my friend could see the files on his desktop, but couldn’t see the “Desktop” folder itself in his home folder.

One place where the HFS+ invisible bit is not honored is the terminal — the ls command lists files and folders regardless of the state of their invisible bits. (The ls command does honor the Unix dot-file convention, though; such files are suppressed unless you use the -a or -A options.)

I’m not aware of any software that ships by default with Mac OS X that lets you see or set the HFS+ invisible bit. [See update below.] If you install the (free) developer tools, though, you can use the GetFileInfo and SetFile utilities.

For example, to check your Desktop folder:

$ GetFileInfo ~/Desktop
directory: "/Users/gruber/Desktop"
attributes: avbstclinmedz
created: 03/30/2008 18:25:34
modified: 04/15/2008 18:55:14

(The first line is what you type at the command line in Terminal; the next four lines are the results.) The GetFileInfo man page explains the “attributes” line: each letter represents an HFS+ metadata attribute. A lowercase letter means the attribute is off/false, an uppercase letter means the attribute is on/true. “V” is the letter for the invisible bit, so, because it’s lowercase in the example output, we can see that the “Desktop” folder is not invisible.

To make the file invisible:

$ SetFile -a "V" Desktop/

Then:

$ GetFileInfo ~/Desktop
directory: "/Users/gruber/Desktop"
attributes: aVbstclinmedz
created: 03/30/2008 18:25:34
modified: 04/15/2008 18:55:14

Note that toggling the invisible bit does not change the folder’s modified date.

Better, for most users, is to use a good file info utility such as Bare Bones Software’s Super Get Info. Just drag a file or folder onto Super Get Info’s icon and you get a nice window showing most of the metadata associated with the item. Invisibility is indicated with a checkbox. Invisible items pose an obvious problem, of course, in that if you can’t see them, you can’t drag them. Super Get Info solves this with its File → Open Hidden command, which brings up an Open dialog box that lists every item in the file system.

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Update: Starting with Leopard, the chflags command now supports “hidden” and “nohidden” options to toggle invisibility:

$ chflags hidden ~/Desktop

On HFS+ volumes, this toggles the invisible bit, just like with SetFile.² Also, you can use the “-lO” (lowercase L and capital O) options with the ls command to include file flags in the output; invisible files will be marked as “hidden”.