Buffers and hidden buffers

Demonstration

Here I have a directory with files named A, B, C, D and E. I’m going to launch Vim in this directory with a wildcard as an argument. This tells Vim to load each file in this directory ending in .txt into a buffer. To begin with, all you can see is the first of these files, but if I run the command:

:ls

then you can see that each of the files has been loaded into a buffer. I can easily scroll through the buffers by running:

:bn[ext]

to view the next buffer, or:

:bp[revious]

to view the previous buffer. Note that previous and next commands do cycle between the first and last items in the buffer list.

Anytime that you run :ls, you get a list of the buffers. These include a few annotations:

• ‘a’ marks an active buffer, meaning that it is currently loaded in a window
• ‘#’ (the hash sign) marks the alternate buffer

You can quickly jump between the active buffer and the alternate buffer using the command: ctrl-^. Pressing it again takes you back to where you were before. You can think of this as being a bit like the command-tab behaviour in OS X (or alt-tab in linux and windows), which switches focus between the currently active window, and the application you used most recently.

Now lets try making a change to file A, without saving it. If I run :ls again, you should see a new symbol:

• + (the plus sign) indicates that a buffer has been modified, therefore its contents differ from the corresponding file

Having made this change, but not saved it, let’s now try and switch to another buffer with the :bn command. This raises an error:

E37: No write since last change (add ! to override)

At this point, I could do a couple of things:

• save the file, and reissue the command to move on to the next buffer
• or follow the advice in the prompt, and run the command with a trailing exclamation mark

Let’s try running :bn! (b-n-bang), as advised. OK, this brings us to the next buffer, as expected. So lets see what happens now when I run :ls

• File A is still marked with a + (plus sign), indicating that the buffer has been modified
• additionally, the file is marked with an ‘h’, which stands for hidden

A buffer is marked as ‘hidden’ if it has unsaved changes, and it is not currently loaded in a window.

Consequences of having hidden buffers

If you try and quit Vim while there are hidden buffers, an error will be raised:

E162: No write since last change for buffer “a.txt:

When you dismiss the error message, you’ll find that the first hidden buffer has been loaded into your current window. This gives you the opportunity to either:

• save the changes to a file (:w)
• restore the original file (:e!)
• or forcibly remove the buffer from the buffer list (:bd!), discarding any changes
• you can also force Vim to quit, discarding changes to all modified buffers (:q!)

By default, Vim makes it difficult for you to create a hidden buffer, but as long as you know how to deal with them when quitting Vim, there’s nothing wrong with creating them. To make Vim use hidden buffers more liberally, I include the following line in my .vimrc:

set hidden

With this setting applied, when I try to navigate away from a buffer with unsaved changes, Vim will automatically hide it. Now, I can run the :bn command, and it will switch to the next buffer without raising an error message.