Comparing Files
The command M-x diff compares two files, displaying the
differences in an Emacs buffer named *diff*. It works by
running the diff program, using options taken from the variable
diff-switches. The value of diff-switches should be a
string; the default is "-c" to specify a context diff.
The buffer *diff* has Compilation mode as its major mode, so
you can use C-x ` to visit successive changed locations in the two
source files. You can also move to a particular hunk of changes and
type <RET> or C-c C-c, or click Mouse-2 on it, to move
to the corresponding source location. You can also use the other
special commands of Compilation mode: <SPC> and <DEL> for
scrolling, and M-p and M-n for cursor motion.
See Compilation.
The command M-x diff-backup compares a specified file with its most
recent backup. If you specify the name of a backup file,
diff-backup compares it with the source file that it is a backup
of.
The command M-x compare-windows compares the text in the current
window with that in the next window. Comparison starts at point in each
window, and each starting position is pushed on the mark ring in its
respective buffer. Then point moves forward in each window, a character
at a time, until a mismatch between the two windows is reached. Then
the command is finished. For more information about windows in Emacs,
Windows.
With a numeric argument, compare-windows ignores changes in
whitespace. If the variable compare-ignore-case is
non-nil, it ignores differences in case as well.
Differences between versions of files are often distributed as
patches, which are the output from diff or a version
control system that uses diff. M-x diff-mode turns on
Diff mode, a major mode for viewing and editing patches, either as
"unified diffs" or "context diffs."
You can use M-x smerge-mode to turn on Smerge mode, a minor
mode for editing output from the diff3 program. This is
typically the result of a failed merge from a version control system
"update" outside VC, due to conflicting changes to a file. Smerge
mode provides commands to resolve conflicts by selecting specific
changes.
See also Emerge, and Top, for
convenient facilities for merging two similar files.
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