Re: How do I specify a revision for "git blame" by date?

Jeff King [off-list ref] writes:

But that still doesn't address the issue that (a) is not well-defined.
Imagine I have this history:

  A--B--C---G--H
   \       /
    D--E--F

that is, two lines of development splitting at A and merging at H. And
imagine the commit timestamps are (let's just refer to them as integers
for the sake of simplicity, but they are representing days or seconds or
whatever):

  A(1)--B(2)--C(3)--G(7)--H(8)
   \               /
    D(2)--E(4)--F(6)

What does it mean to ask for the commit at time=5?
...
Git-blame expects you to give it a well-defined point (as it must, since
it is a backwards walk down history showing what led to a particular set
of content; it wouldn't make sense to feed it multiple starting points).
You could do so by asking rev-list to walk the graph according to your
requirements and feeding the result to blame, like:

  # most recent on any line of development that is merged to HEAD
  git blame `git rev-list -1 --until=5 HEAD`

  # most recent on any line of development in the whole repo
  git blame `git rev-list -1 --until=5 --all`

  # most recent version on the first-parent; if you follow a
  # topic-branch workflow and always merge up into "master", then this
  # will blame what was on master at time=5
  git blame `git rev-list -1 --until=5 --first-parent HEAD`

Very well explained.  Thanks.

The short answer to the question on "Subject:" line is "You don't".

Junio C Hamano [off-list ref] wrote:

Jeff King [off-list ref] writes:

quoted

But that still doesn't address the issue that (a) is not
well-defined.  Imagine I have this history:

  A--B--C---G--H
   \       /
    D--E--F

that is, two lines of development splitting at A and merging
at H. And imagine the commit timestamps are (let's just refer
to them as integers for the sake of simplicity, but they are
representing days or seconds or whatever):

  A(1)--B(2)--C(3)--G(7)--H(8)
   \               /
    D(2)--E(4)--F(6)

What does it mean to ask for the commit at time=5?
...
Git-blame expects you to give it a well-defined point ...
You could do so by asking rev-list to walk the graph according
to your requirements and feeding the result to blame, like:

  # most recent on any line of development that is merged to HEAD
  git blame `git rev-list -1 --until=5 HEAD`

  # most recent on any line of development in the whole repo
  git blame `git rev-list -1 --until=5 --all`

  # most recent version on the first-parent; if you follow a
  # topic-branch workflow and always merge up into "master",
  # then this will blame what was on master at time=5
  git blame `git rev-list -1 --until=5 --first-parent HEAD`

Very well explained.  Thanks.

+1

The short answer to the question on "Subject:" line is "You don't".

The slightly longer, but perhaps more practically useful, answer is
"You use 'git rev-list' to look up the correct commit, and shell
'command substitution' to pass the result to 'git blame', as Jeff
has illustrated."  That solution sure beats displaying the entire
revision list, and then manually selecting the desired commit from
it.