Re: git-diff between /dev/null and blob

From: Junio C Hamano <junkio@cox.net>
Date: Aug 6, 2006, 21:36 UTC
Message-ID: <7vejvt8s24.fsf@assigned-by-dhcp.cox.net>
In-Reply-To: <eb5ld6$36k$1@sea.gmane.org>

Jakub Narebski <jnareb@gmail.com> writes:

Show 16 quoted lines

> Junio C Hamano wrote:
>
>> Jakub Narebski <jnareb@gmail.com> writes:
>> 
>>> Currently, due to artifact of git-diff argument parsing you can get diff 
>>> of two arbitrary blobs given by their sha1 id, e.g.
>>>   git diff ab8050ceb4e43522e858768cc2c02fcb91839370 fd05278808d458602587bb024a48726018d30926
>> 
>> Just FYI, it is pretty much by design not artifact to allow
>> something like this:
>> 
>>       git diff master:Makefile next:Makefile
>
> Which we could get using
>
>         git diff master next -- Makefile

Eh, that comment completely misses the point, because the example did not show its true strength. Arbitrary two blob sha1 lets you do something like this:

	git diff v0.99:merge-cache.c master:merge-index.c
	git diff v0.99:pull.h fetch.h

        echo extra >>Makefile && git diff :0:Makefile HEAD^^:Makefile

        H=`(cat Makefile; echo extra) | git hash-object -w --stdin`
	echo "100644 $H 2	foobar" | git update-index --add --index-info
	git diff :2:foobar :Makefile

> git-diff doesn't understand :<stage>:<filename> and :<filename> for
> accessing index version of blob (git-cat-file for example understands
> it).

You probably got this impression from a botched experiment or something, but this statement is wrong as demonstrated above.