23.7.4 Examining And Comparing Old Versions
One of the convenient features of version control is the ability
to examine any version of a file, or compare two versions.
- C-x v ~ version <RET>
- Examine version version of the visited file, in a buffer of its
- C-x v =
- Compare the current buffer contents with the latest checked-in version
of the file.
- C-u C-x v = file <RET> oldvers <RET> newvers <RET>
- Compare the specified two versions of file.
- C-x v g
- Display the file with per-line version information and using colors.
To examine an old version in its entirety, visit the file and then type
C-x v ~ version <RET> (
This puts the text of version version in a file named
filename.~version~, and visits it in its own buffer
in a separate window. (In RCS, you can also select an old version
and create a branch from it. See Branches.)
It is usually more convenient to compare two versions of the file,
with the command C-x v = (
vc-diff). Plain C-x v =
compares the current buffer contents (saving them in the file if
necessary) with the last checked-in version of the file. C-u C-x
v =, with a numeric argument, reads a file name and two version
numbers, then compares those versions of the specified file. Both
forms display the output in a special buffer in another window.
You can specify a checked-in version by its number; an empty input
specifies the current contents of the work file (which may be different
from all the checked-in versions). You can also specify a snapshot name
(see Snapshots) instead of one or both version numbers.
If you supply a directory name instead of the name of a registered
file, this command compares the two specified versions of all registered
files in that directory and its subdirectories.
C-x v = works by running a variant of the
designed to work with the version control system in use. When you
diff this way, in addition to the options specified by
diff-switches (see Comparing Files), it receives those
vc-diff-switches, plus those specified for the
specific back end by
instance, when the version control back end is RCS,
the options in
‘vc...diff-switches’ variables are
nil by default.
Unlike the M-x diff command, C-x v = does not try to
locate the changes in the old and new versions. This is because
normally one or both versions do not exist as files when you compare
them; they exist only in the records of the master file.
See Comparing Files, for more information about M-x diff.
For some backends, you can display the file annotated with
per-line version information and using colors to enhance the visual
appearance, with the command M-x vc-annotate.
It creates a new buffer
to display file's text, colored to show how old each part is. Text
colored red is new, blue means old, and intermediate colors indicate
intermediate ages. By default, the time scale is 360 days, so that
everything more than one year old is shown in blue.
When you give a prefix argument to this command, it uses the
minibuffer to read two arguments: which version number to display and
annotate (instead of the current file contents), and a stretch factor
for the time scale. A stretch factor of 0.1 means that the color
range from red to blue spans the past 36 days instead of 360 days. A
stretch factor greater than 1 means the color range spans more than a
From the annotate buffer, you can use the following keys to browse the
annotations of past revisions, view diffs, or view log entries:
- Annotate the previous revision, that is to say, the revision before
the one currently annotated. A numeric prefix argument is a repeat
count, so C-u 10 P would take you back 10 revisions.
- Annotate the next revision—the one after the revision currently
annotated. A numeric prefix argument is a repeat count.
- Annotate the revision indicated by the current line.
- Annotate the revision before the one indicated by the current line.
This is useful to see the state the file was in before the change on
the current line was made.
- Display the diff between the current line's revision and the previous
revision. This is useful to see what the current line's revision
actually changed in the file.
- Show the log of the current line's revision. This is useful to see
the author's description of the changes in the revision on the current
- Annotate the workfile version–the one you are editing. If you used
P and N to browse to other revisions, use this key to
return to the latest version.