Take Control of Your Buffers With Ibuffer-Mode

The buffer is a basic data structure in Emacs. As a Text User Interface (TUI) platform, everything you interact with is stored as text in a buffer, whether that is code you are developing, a blog post you are writing, or the input to and output from an interactive shell.

As your Emacs session goes on, as you visit files and run programs and do all the things you can do with it, buffers start piling up. They seem to come from nowhere, and before you know it, you are finding them behind the couch, under your bed, you trip over them in the hall. And then when you need to switch back to a buffer that you last looked at the day before, you have to sift through that pile to find the one you want.

A quick C-x C-b brings up Emacs's default buffer manager, buffer-menu-mode. It is a fairly straightforward mode, which lists all open buffers, allows you to jump to any particular one, to save or delete a group of buffer, and other basic buffer-related tasks. Good enough when getting started with Emacs.

But once you've been working in Emacs long enough and your open buffers start piling up, buffer-menu-mode no longer cuts it. The more clothes you have, the more you are in need of a way to organize them, to put them away into drawers, to have a system that makes sense out of the chaos. And the same is true for your buffers.

Fortunately, Emacs provides a better alternative, called ibuffer-mode, included in GNU Emacs as of version 22. To give it a try, simply run M-x ibuffer to open a new buffer in ibuffer-mode. It shares a number of similarities with dired mode, and therefore should be easy to pick up and start performing simple operations on buffers.

In the above image you will notice that buffers are grouped into sets under a label, a feature we will discuss later in this post.

Like the default buffer-menu-mode, ibuffer-mode provides a visualization of the current set of buffers and a set of operations you can perform on them. These include operations on individual buffers and sets of selected, or "marked", buffers, as well as operations on the content of a single or set of buffers. The individual buffer commands include removing them, searching their contents, sending their contents to a shell command, and other useful operations. The buffer group operations are where it really becomes a powerful tool. These include:

• Marking
• Filtering
• Grouping
• Sorting

Marking

Marking is a simple concept that translates from other commonly used Emacs modes such as dired. It provides a way to perform operations on multiple objects, in this case buffers, by selecting them individually and then applying an operation to the currently marked set.

Want to delete a set of buffers all at once? Mark them for deletion by moving point to each and hitting d, then hit x to execute. Want to perform an incremental search through multiple buffers at one time? Mark each one then hit M-s a C-s and start typing your search term. There are also commands to do search and replace operations, or to evaluate a lisp form in each. And as always, a simple C-h m brings up the mode's help buffer so you can get all the details.

Filtering

Ibuffer-mode has powerful and flexible filtering capabilities, allowing you to narrow down the set of displayed buffers with myriad options for filtering criteria.

Filtering commands are all prefixed with a slash: /, followed by a single character which determines the kind of filter to apply. You can filter by criteria such as buffer name, major or minor mode, directory, modified status, file extension, and more.

Going beyond the application of a simple filter, things get interesting, because filters can be combined into filter pipelines in which they are applied one after the other to get the desired result, and pipelines can be manipulated to easily switch between different views of your set of open buffers.

Filtering Example

As an example, let's say you want to filter your buffer list down to just the "starred" buffers, the ones that are by convention surrounded by the asterisk symbol to indicate that they were created by Emacs itself. Hit / * to apply that filter:

Then you realize you'd like to view all of your Org Mode buffers at the same time. Add that filter with / RET org-mode. Now the buffer list is empty since there are no filters that pass both tests:

What you want is to apply both filters separately and combine the results, using a logical "OR" so that you see those buffers that are either starred or org-mode. And that is as easy as hitting / | after having previously inserted both into the pipeline.

AND'ing filters together is also possible with / &.

That is a simple example of what is possible in terms of applying filters to your buffer list, and of course there is plenty more to discover for the curious.

Before we move on to other features of ibuffer-mode, we should also point out that if you have a filter or set of filters that you use often or don't want to have to recreate each time you need them, ibuffer-mode allows you to save named filters for later retrieval. Hit / s to bring up the prompt to save your current set of filters under a user-chosen name, and then / r to find and re-apply it.

In my exploration of buffer management in Emacs, I've found that there are even a few more options than the basic buffer-menu and ibuffer-modes I've discussed here. You can add to that list buffer-selection-menu and electric-buffer-menu, which can be be accessed with M-x bs-show and M-x electric-buffer-list, respectively. Both of these sit somewhere between buffer-menu and ibuffer modes in terms of what they offer the Emacs user, and so I don't think there is any reason to go into them here, but mention them just to complete the picture.

There you have it, another way to make your Emacs experience better. Since you are always working with buffers in Emacs, a better buffer handler is a big help.

Below is some elisp code to get you started with ibuffer- mode, taken mostly right from the Emacs Wiki:

  ; Use ibuffer-mode as the default buffer handler
  (global-set-key (kbd "C-x C-b") 'ibuffer)

  ; Add a saved filter group to apply to your Ibuffer menu
  (setq ibuffer-saved-filter-groups
        '(("Home"
       	  ("Dired" (mode . dired-mode))
    	  ("Customizations" (mode . custom-mode))
    	  ("Org Mode" (or (filename . ".org") (mode . org-mode)))
    	  ("Starred" (starred-name)))))

  ; Apply your saved filter group automatically when opening
  ; ibuffer-mode
  (add-hook 'ibuffer-mode-hook
    	  (lambda ()
    	    (ibuffer-switch-to-saved-filter-groups "Home")))

• Emacs Wiki entry for IbufferMode
• Online documentation