How to say HEAD~"all the way back - 1"

How to say HEAD~"all the way back - 1"

[Bill Lear]

Git "indexing" of commits has a way to "go back":

% git diff HEAD~3

Can I say "all the way back", or "all the way back - 1" somehow?


Bill

Re: How to say HEAD~"all the way back - 1"

[Petr Baudis]

On Thu, Feb 22, 2007 at 08:17:17PM CET, Bill Lear wrote:
> Git "indexing" of commits has a way to "go back":
> 
> % git diff HEAD~3
> 
> Can I say "all the way back", or "all the way back - 1" somehow?

What would that mean? :)

Do you mean to the "root" of the history? The trouble is, there can be
many of such roots (coming up from merges of previously disjunct
histories); even the git project itself has several. Which one to
choose?

-- 
				Petr "Pasky" Baudis
Stuff: http://pasky.or.cz/
The meaning of Stonehenge in Traflamadorian, when viewed from above, is:
"Replacement part being rushed with all possible speed."
		-- Kurt Vonnegut, Sirens from Titan

Re: How to say HEAD~"all the way back - 1"

[Jakub Narebski]

Petr Baudis wrote:

> On Thu, Feb 22, 2007 at 08:17:17PM CET, Bill Lear wrote:
>> Git "indexing" of commits has a way to "go back":
>> 
>> % git diff HEAD~3
>> 
>> Can I say "all the way back", or "all the way back - 1" somehow?
> 
> What would that mean? :)
> 
> Do you mean to the "root" of the history? The trouble is, there can be
> many of such roots (coming up from merges of previously disjunct
> histories); even the git project itself has several. Which one to
> choose?

Actually HEAD~n follows first parent, so it would be only one such root.

The git project has 4 or 5 roots for mainline + 3 separate disjoint 
branches with separate roots (html, man, todo).

-- 
Jakub Narebski
Warsaw, Poland
ShadeHawk on #git

Re: How to say HEAD~"all the way back - 1"

[Bill Lear]

On Friday, February 23, 2007 at 18:52:22 (+0100) Jakub Narebski writes:
>Petr Baudis wrote:
>
>> On Thu, Feb 22, 2007 at 08:17:17PM CET, Bill Lear wrote:
>>> Git "indexing" of commits has a way to "go back":
>>> 
>>> % git diff HEAD~3
>>> 
>>> Can I say "all the way back", or "all the way back - 1" somehow?
>> 
>> What would that mean? :)
>> 
>> Do you mean to the "root" of the history? The trouble is, there can be
>> many of such roots (coming up from merges of previously disjunct
>> histories); even the git project itself has several. Which one to
>> choose?
>
>Actually HEAD~n follows first parent, so it would be only one such root.

Exactly what I was after.  Something like:

% git diff HEAD~-1

or

% git diff ^HEAD~0

whatever ...


Bill

Re: How to say HEAD~"all the way back - 1"

[Junio C Hamano]

Bill Lear <rael@zopyra.com> writes:

> Exactly what I was after.  Something like:
>
> % git diff HEAD~-1
>
> or
>
> % git diff ^HEAD~0
>
> whatever ...

<amusement>

        $ git rev-parse HEAD~4096
        fatal: ambiguous argument 'HEAD~4096': unknown revision or path ...
        $ git rev-parse HEAD~2048
        231af8322...
        $ git rev-parse HEAD~3072
        723c31fea...
        $ git rev-parse HEAD~3584
        ....
        $ git rev-parse HEAD_3952
        e83c5163316f89bfbde7d9ab23ca2e25604af290

</amusement>

If you somehow need to know where the root is all the time, you
could do the above once and say:

	$ git tag root-commit e83c5163316f89bfbde7d9ab23ca2e25604af290

Re: How to say HEAD~"all the way back - 1"

[Junio C Hamano]

Bill Lear <rael@zopyra.com> writes:

> Git "indexing" of commits has a way to "go back":
>
> % git diff HEAD~3
>
> Can I say "all the way back", or "all the way back - 1" somehow?

Sorry, there is no such shorthand, but you could obviously say:

	$ git rev-list --parents HEAD | grep -v ' '

A way to find the root commit seems to be one of the things
people new to git want at least once, once they start futzing
with the tool.  But I suspect that is only because they need
that information to see how the tool works (say "what different
output would I get out of 'git show $commit' for root and other
commits?"), and not because they need that information for any
real life use.

Really, what useful purpose does it serve for you to find out
the root commit, OTHER THAN being able to say "the development
history of this project starts at this commit"?

Re: How to say HEAD~"all the way back - 1"

[Bill Lear]

On Thursday, February 22, 2007 at 12:12:45 (-0800) Junio C Hamano writes:
>Bill Lear <rael@zopyra.com> writes:
>
>> Git "indexing" of commits has a way to "go back":
>>
>> % git diff HEAD~3
>>
>> Can I say "all the way back", or "all the way back - 1" somehow?
>
>Sorry, there is no such shorthand, but you could obviously say:
>
>	$ git rev-list --parents HEAD | grep -v ' '
>
>A way to find the root commit seems to be one of the things
>people new to git want at least once, once they start futzing
>with the tool.  But I suspect that is only because they need
>that information to see how the tool works (say "what different
>output would I get out of 'git show $commit' for root and other
>commits?"), and not because they need that information for any
>real life use.
>
>Really, what useful purpose does it serve for you to find out
>the root commit, OTHER THAN being able to say "the development
>history of this project starts at this commit"?

Just today, I got a bug report from one of our developers.
The git update hook we had in place before the conversion
to 1.5 had this:

chmod -R ug+w $GIT_DIR

to avoid problems when people used 'git ssh://...", due to
different umasks (yeah, a hack).

So, moving to 1.5, I updated our script (and, had been updating it for
quite some time, so many revisions, maybe 20 or so), and well,
now when people use ssh, they leave behind directories others
can't read (as git now allows push through "git://", we'll be
weaning people off of ssh soon).

So, I wanted to say "give me the first version of this, so I
can cut-n-paste the chmod command, since I can't remember if it
was chmod, or chown, or some combination ...", and thus the desire
to to:

% git log -p HEAD~"All the way back" update

or something similar.


Bill

Re: How to say HEAD~"all the way back - 1"

[Junio C Hamano]

Bill Lear <rael@zopyra.com> writes:

> % git log -p HEAD~"All the way back" update
>
> or something similar.

But in that use case "root" commit is not necessarily what you
wanted to say, isn't it?  It is more like "I want *earlier*
history, not latest ones as the command usually gives, of this
file".

$ git log --reverse -p HEAD -- update

would give you the changes that touch the path in the reverse
order than usual (I think this was merged post 1.5.0).

But my point is, you may happen to know it was in your root
commit, but that is a special case.  You may happen to know
other things to limit the output.  The timeperiod you made that
change (e.g. --until=2006-05-31), for example.

By the way, on the face of it:

$ git log --reverse -4 -p HEAD -- update

(or whatever number of commits you are interested in viewing)
might be closer to what you want to express, but the --reverse
option does not work like that, unfortunately for this
particular use case, because the way the semantics of
interaction between --reverse and --max-count is defined.

Given the above command line, the current implementation limits
the traversal to four items and then reverses the output,
instead of traversing normally as if --max-count limitation is
not there, reversing the result and then limiting the output to
four items, which would have made the sample command line above
a bit more useful.

But I would recommend against changing it.  Being able to view
the latest four commits in reverse is much more useful in
practice than being able to view the four commits at the
beginning of time in reverse.  Having both options is certainly
a possibility but I doubt it is worth it.

Re: How to say HEAD~"all the way back - 1"

[J. Bruce Fields]

On Thu, Feb 22, 2007 at 12:12:45PM -0800, Junio C Hamano wrote:
> Sorry, there is no such shorthand, but you could obviously say:
> 
> 	$ git rev-list --parents HEAD | grep -v ' '
> 
> A way to find the root commit seems to be one of the things
> people new to git want at least once, once they start futzing
> with the tool.  But I suspect that is only because they need
> that information to see how the tool works (say "what different
> output would I get out of 'git show $commit' for root and other
> commits?"), and not because they need that information for any
> real life use.
> 
> Really, what useful purpose does it serve for you to find out
> the root commit, OTHER THAN being able to say "the development
> history of this project starts at this commit"?

I occasionally want to reference commits not relative to "all the way
back" but to "all the way back on this branch".  So, e.g., what's the
next-to-last commit before "topic" meets up with "origin"?

I can do something like

	git rev-list origin..topic | tail -2 | head -1

but in practice it's faster just to fire up gitk origin.. and
cut-n-paste object id's.

--b.

Re: How to say HEAD~"all the way back - 1"

[Johannes Schindelin]

Hi,

On Thu, 22 Feb 2007, J. Bruce Fields wrote:

> I can do something like
> 
> 	git rev-list origin..topic | tail -2 | head -1
> 
> but in practice it's faster just to fire up gitk origin.. and
> cut-n-paste object id's.

Or something like

	git rev-list --reverse origin..topic | sed -n 2p

But that's even longer! (Although conceptually shorter...)

Ciao,
Dscho