git-checkout older revision of a file under a new name

I have the file "main.cpp" open in my editor.

I want to see the previous revision of "main.cpp" in the editor too.

The way I do it now is like this.

close "main.cpp" in the editor

prompt> mv main.cpp tmp
prompt> git checkout HEAD^ main.cpp
prompt> mv main.cpp old_main.cpp
prompt> mv tmp main.cpp
prompt>

open "main.cpp" and "old_main.cpp" in the editor

Can it be simplified, so I don't have to close "main.cpp" in the editor?

What I'm hoping for is a variant of git-checkout that can do this.

---

UPDATE: im using git on mac osx 10.5.7

prompt> git --version
git version 1.6.0.4
prompt> 

---

UPDATE2: Jakub Narębski answer is:

prompt> git show HEAD^:dir1/dir2/dir3/main.cpp > old_main.cpp
prompt>

---

UPDATE3: Karmi's answer, for a specific revision:

prompt> git show 4c274dd91dc:higgs/Higgs.xcodeproj/project.pbxproj > old_project.pbxproj
prompt> 

You can use git show for that:

git show HEAD^:main.cpp > old_main.cpp

(Note that there is colon [:] character between HEAD^ and main.cpp.) The <revision>:<path> syntax is described in [git rev-parse][git-rev-parse] manpage, next to last point in the "Specifying revisions" section:

> <rev>:<path>, e.g. HEAD:README, :README, master:./README > > A suffix : followed by a path names the blob or tree at the given path in the tree-ish > object named by the part before the colon. :path (with an empty part before the colon) > is a special case of the syntax described next: content recorded in the index at the > given path. A path starting with ./ or ../ is relative to the current working directory. > The given path will be converted to be relative to the working tree’s root directory. > This is most useful to address a blob or tree from a commit or tree that has the same > tree structure as the working tree.

Note that <path> here is FULL path relative to the top directory of your project, i.e. the directory with .git/ directory. (Or, to be more exact, to "<revision>", which in general can be any <tree-ish>, i.e. something that represents tree.)

If you want to use path relative to the current directory, you need to use ./<path> syntax (or ../path to go up from current directory).

^{Edit 2015-01-15: added information about relative path syntax}

---

You can get in most cases the same output using low-level (plumbing) git cat-file command:

git cat-file blob HEAD^:main.cpp > old_main.cpp

[git-rev-parse]: http://www.kernel.org/pub/software/scm/git/docs/git-rev-parse.html "git-rev-parse(1) Manual Page"

Just to add to Jakub's answer: you don't even have to redirect the output to a file with >, if you are only interested in skimming the file contents in the terminal. You can just run $ git show 58a3db6:path/to/your/file.txt.

Singular use case

In order to get consistent checkout behavior including autocrlf etc., use a secondary folder (TEMP as example) and restore the file state from an older / different like this:

git --work-tree TEMP/ restore -s <commit> main.cpp
mv TEMP/main.cpp old_main.cpp

Note:

git show <commit>:main.cpp > old_main.cpp

.. will just produce a raw read from the repository.

Use a 2nd work tree - anonymous or linked

For more comfort working with alternative file states (without the need for renaming) use a secondary "anonymous" directory as a (long term) parallel work tree like this:

# one time setup
mkdir WD2
cd WD2
echo gitdir: WD1 > .git

# operate freely here with an alternative file set while the same branch is checked out in git
git restore -s <commit> main.cpp

(WD2 : path to secondary dir. WD1 : path to primary dir - Absolute or relative)

Note: Any kind of git project work (restore / add / commit / switch ..., build tasks) can be done with that alternative file set - as if suddenly the work tree files in WD1 would have been swapped. Hard links could be used for efficiently mirroring unchanged files in huge repos.

Similarly a "linked working tree" can be used via git-worktree (new since git v2.6.7). This causes somewhat more git overhead, but allows to checkout and work on a different branch (or detached head) simultaneously without using an extra repo.