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(emacs)Old Versions

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Examining And Comparing Old Versions
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   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
     own.

`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 result of the CVS annotate command using colors.

   To examine an old version in its entirety, visit the file and then
type `C-x v ~ VERSION <RET>' (`vc-version-other-window').  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.  Note:
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
(Note: 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 `diff' utility designed
to work with the version control system in use.  When you invoke `diff'
this way, in addition to the options specified by `diff-switches'
(Note: Comparing Files), it receives those specified by
`vc-diff-switches', plus those specified for the specific back end by
`vc-BACKEND-diff-switches'.  For instance, when the version control
back end is RCS, `diff' uses the options in `vc-rcs-diff-switches'.  The
`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.  Note: Comparing Files, for
more information about `M-x diff'.

   For CVS-controlled files, you can display the result of the CVS
annotate command, using colors to enhance the visual appearance.  Use
the command `M-x vc-annotate' to do this.  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 year.