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

Question 1

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>

Question 2

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 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-checkout older revision of a file under a new name

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