ediff: Introduction
1 Introduction
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Ediff provides a convenient way for simultaneous browsing through the
differences between a pair (or a triple) of files or buffers (which are
called ‘variants’ for our purposes). The files being compared, file-A,
file-B, and file-C (if applicable) are shown in separate windows (side
by side, one above the another, or in separate frames), and the
differences are highlighted as you step through them. You can also copy
difference regions from one buffer to another (and recover old
differences if you change your mind).
Another powerful feature is the ability to merge a pair of files into
a third buffer. Merging with an ancestor file is also supported.
Furthermore, Ediff is equipped with directory-level capabilities that
allow the user to conveniently launch browsing or merging sessions on
groups of files in two (or three) different directories.
In addition, Ediff can apply a patch to a file and then let you step
through both files, the patched and the original one, simultaneously,
difference-by-difference. You can even apply a patch right out of a
mail buffer, i.e., patches received by mail don’t even have to be saved.
Since Ediff lets you copy differences between variants, you can, in
effect, apply patches selectively (i.e., you can copy a difference
region from ‘file.orig’ to ‘file’, thereby undoing any particular patch
that you don’t like).
Ediff even understands multi-file patches and can apply them
interactively! (Ediff can recognize multi-file patches only if they are
in the context format or GNU unified format. All other patches are
treated as 1-file patches. Ediff is [hopefully] using the same
algorithm as ‘patch’ to determine which files need to be patched.)
Ediff is aware of version control, which lets you compare files with
their older versions. Ediff also works with remote and compressed
files, automatically ftp’ing them over and uncompressing them. 
Remote and Compressed Files, for details.
This package builds upon ideas borrowed from Emerge, and several of
Ediff’s functions are adaptations from Emerge. Although Ediff subsumes
and greatly extends Emerge, much of the functionality in Ediff is
influenced by Emerge. The architecture and the interface are, of
course, drastically different.
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