As you saw in the section called “Revisions”, revision numbers in Subversion are pretty straightforward—integers that keep getting larger as you commit more changes to your versioned data. Still, it doesn't take long before you can no longer remember exactly what happened in each and every revision. Fortunately, the typical Subversion workflow doesn't often demand that you supply arbitrary revisions to the Subversion operations you perform. For operations that do require a revision specifier, you generally supply a revision number that you saw in a commit email, in the output of some other Subversion operation, or in some other context that would yield meaning to that particular number.
But occasionally, you need to pinpoint a moment in time for which you don't already have a revision number memorized or handy. So besides the integer revision numbers, svn allows as input some additional forms of revision specifiers—revision keywords, and revision dates.
The various forms of Subversion revision specifiers can be
mixed and matched when used to specify revision ranges. For
example, you can use -r
where REV1:REV2REV1 is a revision keyword
and REV2 is a revision number, or
where REV1 is a date and
REV2 is a revision keyword, and so
on. The individual revision specifiers are independently
evaluated, so you can put whatever you want on the opposite
sides of that colon.
The Subversion client understands a number of
revision keywords. These keywords can
be used instead of integer arguments to the
--revision (-r) switch, and are resolved into
specific revision numbers by Subversion:
The latest (or “youngest”) revision in the repository.
The revision number of an item in a working copy. If the item has been locally modified, the “BASE version” refers to the way the item appears without those local modifications.
The most recent revision prior to, or equal to,
BASE, in which an item changed.
The revision immediately before
the last revision in which an item changed.
Technically, this boils down to
COMMITTED-1.
As can be derived from their descriptions, the
PREV, BASE, and
COMMITTED revision keywords are used only
when referring to a working copy path—they don't apply
to repository URLs. HEAD, on the other
hand, can be used in conjuction with both of these path
types.
Here are some examples of revision keywords in action:
$ svn diff -r PREV:COMMITTED foo.c # shows the last change committed to foo.c $ svn log -r HEAD # shows log message for the latest repository commit $ svn diff -r HEAD # compares your working copy (with all of its local changes) to the # latest version of that tree in the repository $ svn diff -r BASE:HEAD foo.c # compares the unmodified version of foo.c with the latest version of # foo.c in the repository $ svn log -r BASE:HEAD # shows all commit logs for the current versioned directory since you # last updated $ svn update -r PREV foo.c # rewinds the last change on foo.c, decreasing foo.c's working revision $ svn diff -r BASE:14 foo.c # compares the unmodified version of foo.c with the way foo.c looked # in revision 14
Revision numbers reveal nothing about the world outside
the version control system, but sometimes you need to
correlate a moment in real time with a moment in version
history. To facilitate this, the --revision (-r)
option can also accept as input date specifiers wrapped in
curly braces ({ and }).
Subversion accepts the standard ISO-8601 date and time
formats, plus a few others. Here are some examples.
(Remember to use quotes around any date that contains
spaces.)
$ svn checkout -r {2006-02-17}
$ svn checkout -r {15:30}
$ svn checkout -r {15:30:00.200000}
$ svn checkout -r {"2006-02-17 15:30"}
$ svn checkout -r {"2006-02-17 15:30 +0230"}
$ svn checkout -r {2006-02-17T15:30}
$ svn checkout -r {2006-02-17T15:30Z}
$ svn checkout -r {2006-02-17T15:30-04:00}
$ svn checkout -r {20060217T1530}
$ svn checkout -r {20060217T1530Z}
$ svn checkout -r {20060217T1530-0500}
…
When you specify a date, Subversion resolves that date to the most recent revision of the repository as of that date, and then continues to operate against that resolved revision number:
$ svn log -r {2006-11-28}
------------------------------------------------------------------------
r12 | ira | 2006-11-27 12:31:51 -0600 (Mon, 27 Nov 2006) | 6 lines
…
You can also use a range of dates. Subversion will find all revisions between both dates, inclusive:
$ svn log -r {2006-11-20}:{2006-11-29}
…
Since the timestamp of a revision is stored as an unversioned, modifiable property of the revision (see the section called “Properties”, revision timestamps can be changed to represent complete falsifications of true chronology, or even removed altogether. This will wreak havoc on the internal date-to-revision conversion that Subversion performs.