'git show' with multiple revisions

I would like to see the content of a file in multiple revisions. I can get them with 'git show' as follows:

    % git show REV1:FILE
    % git show REV2:FILE

and so on. But that launches a new process for each revision. Now, there is the option to pass multiple arguments to 'git show':

    % git show REV1:FILE REV2:FILE

This gets both revisions in a single process and so is faster. But it concatenates the content so there isn't a way to separate them out again.

Could 'git show' sprout an option to get multiple things programmatically so that they can be separated out again? One way would be to quote or escape the contents somehow so that the result can be parsed:

    % git show --porcelain REV1:FILE REV2:FILE

The question is what format should be used to output many strings to stdout.

An alternative would be to specify an output file:

    % git show --output foo REV1:FILE                        # writes foo
    % git show --output foo REV1:FILE --output bar REV2:FILE # writes foo, bar

Note that here I am only getting the file content, not log messages or any of the other things which 'git show' can produce. So perhaps what I really want is some kind of 'git cat'. Or is there another more appropriate tool?

Thanks,

On Tue, Apr 28, 2015 at 10:10:52AM +0000, Ed Avis wrote:

I think you want `git cat-file`:

  {
	echo REV1:FILE
	echo REV2:FILE
  } |
  git cat-file --batch

This prints a header line for each output object which contains the size of the object (so a parser reads a header line, then N bytes, then a header line, N bytes, and so on).

-Peff

Jeff King <peff <at> peff.net> writes:

This looks like what I want but the object ids printed appear to be the id of the file in a given revision - not the id of the revision itself. So the ids in the output are not the same as the ones in the input.

That's fine, as long as I can assume that the output entries are in the same order as the input?

On Wed, Apr 29, 2015 at 03:47:33PM +0000, Ed Avis wrote:

Correct. You are feeding a name which resolves to the blob sha1, so that's what cat-file will output for the object id.

Yes, it will process and output them in order.

-Peff

Ed Avis <eda@waniasset.com> writes:

Actually you are asking for REV1:FILE and REV2:FILE, and you are getting these object IDs in the output (you are not asking for REV1 or REV2 henace you will not see these commit object IDs).

"cat-file --batch" will give you the objects in the order you ask. I _think_ you can even do that interactively (i.e. you spawn the process, you feed one object name to its input, you consume its output by reading the header and then given number of bytes, and then you feed the next object name to its input, and so on) without deadlocking yourself.

Junio C Hamano <gitster <at> pobox.com> writes:

Thanks, that makes it easy to deal with. In fact, I might prefer to use git cat-file --batch-check and then use some other library to fetch the blob contents.

Ed Avis <eda@waniasset.com> writes:

If all you need is a translation from extended SHA-1 object name like HEAD~243:Documentation/README to the raw 40-hex object name, "rev-parse" may turn out to be more suitable tool than that.

It of course depends on your use case.