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7.12 Miscellaneous

Here are a few other variables for customizing Ediff:

ediff-split-window-function
Controls the way you want the window be split between file-A and file-B (and file-C, if applicable). It defaults to the vertical split (split-window-vertically, but you can set it to split-window-horizontally, if you so wish. Ediff also lets you switch from vertical to horizontal split and back interactively.

Note that if Ediff detects that all the buffers it compares are displayed in separate frames, it assumes that the user wants them to be so displayed and stops splitting windows. Instead, it arranges for each buffer to be displayed in a separate frame. You can switch to the one-frame mode by hiding one of the buffers A/B/C.

You can also swap the windows where buffers are displayed by typing ~.

ediff-merge-split-window-function
Controls how windows are split between buffers A and B in the merge mode. This variable is like ediff-split-window-function, but it defaults to split-window-horizontally instead of split-window-vertically.
ediff-make-wide-display-function
The value is a function to be called to widen the frame for displaying the Ediff buffers. See the on-line documentation for ediff-make-wide-display-function for details. It is also recommended to look into the source of the default function ediff-make-wide-display.

You can toggle wide/regular display by typing m. In the wide display mode, buffers A, B (and C, when applicable) are displayed in a single frame that is as wide as the entire workstation screen. This is useful when files are compared side-by-side. By default, the display is widened without changing its height.

ediff-use-last-dir
Controls the way Ediff presents the default directory when it prompts the user for files to compare. If nil, Ediff uses the default directory of the current buffer when it prompts the user for file names. Otherwise, it will use the directories it had previously used for files A, B, or C, respectively.
ediff-no-emacs-help-in-control-buffer
If t, makes C-h behave like the <DEL> key, i.e., it will move you back to the previous difference rather than invoking help. This is useful when, in an xterm window or a text-only terminal, the Backspace key is bound to C-h and is positioned more conveniently than the <DEL> key.
ediff-toggle-read-only-function
This variable's value is a function that Ediff uses to toggle the read-only property in its buffers.

The default function that Ediff uses simply toggles the read-only property, unless the file is under version control. For a checked-in file under version control, Ediff first tries to check the file out.

ediff-make-buffers-readonly-at-startup nil
If t, all variant buffers are made read-only at Ediff startup.
ediff-keep-variants
The default is t, meaning that the buffers being compared or merged will be preserved when Ediff quits. Setting this to nil causes Ediff to offer the user a chance to delete these buffers (if they are not modified). Supplying a prefix argument to the quit command (q) temporarily reverses the meaning of this variable. This is convenient when the user prefers one of the behaviors most of the time, but occasionally needs the other behavior.

However, Ediff temporarily resets this variable to t if it is invoked via one of the "buffer" jobs, such as ediff-buffers. This is because it is all too easy to lose a day's work otherwise. Besides, in a "buffer" job, the variant buffers have already been loaded prior to starting Ediff, so Ediff just preserves status quo here.

Using ediff-cleanup-hook, one can make Ediff delete the variants unconditionally (e.g., by making ediff-janitor into one of these hooks).

ediff-keep-tmp-versions
Default is nil. If t, the versions of the files being compared or merged using operations such as ediff-revision or ediff-merge-revisions are not deleted on exit. The normal action is to clean up and delete these version files.
ediff-grab-mouse
Default is t. Normally, Ediff grabs mouse and puts it in its control frame. This is useful since the user can be sure that when he needs to type an Ediff command the focus will be in an appropriate Ediff's frame. However, some users prefer to move the mouse by themselves. The above variable, if set to maybe, will prevent Ediff from grabbing the mouse in many situations, usually after commands that may take more time than usual. In other situation, Ediff will continue grabbing the mouse and putting it where it believes is appropriate. If the value is nil, then mouse is entirely user's responsibility. Try different settings and see which one is for you.