Multiple consecutive null bytes with log -z --name-only

Multiple consecutive null bytes with log -z --name-only

[Drew Noakes]

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Hi all,

I'm a developer on the Git Extensions project [1] and am looking at an
issue parsing the output of `git log` in that application.

Some investigation suggests that a certain combination of arguments causes
multiple consecutive null bytes between rows, where I would ordinarily
expect one.

Passing -z with --name-only causes double nulls.

$ git log -z --pretty=format:"%H" --name-only | grep -obUaP "\x00\x00" | wc
-l
8994
$ git log -z --pretty=format:"%H" | grep -obUaP "\x00\x00" | wc -l
0

We can work around this issue, but I would like to understand if it's a bug
or if there's some information to be gleaned here.

$ git --version
git version 2.18.0.windows.1

Many thanks,

Drew

[1] https://github.com/gitextensions/gitextensions

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Re: Multiple consecutive null bytes with log -z --name-only

[Junio C Hamano]

Drew Noakes <drew@drewnoakes.com> writes:

> Passing -z with --name-only causes double nulls.
>
> $ git log -z --pretty=format:"%H" --name-only | grep -obUaP "\x00\x00" | wc
> -l
> 8994
> $ git log -z --pretty=format:"%H" | grep -obUaP "\x00\x00" | wc -l
> 0

With --pretty that tells you to show %H and --name-only that tells
you to show names of paths that were touched by each commit, you'd
need to be able to distinguish commit object name (or whategver you
give --pretty=format to) and each pathname, and because you are
driving "log", you also should be able to see where info for one
commit ends and the next one starts.

So I'd imagine that for a commit that touches N paths, you would get
(one pathname followed by NUL) N times, and then another NUL after
that to let you know that you read all the pathnames for that
commit.

By the way, tools should be reading from "--format=...", not from
"--pretty=format:...".  The --format=... option is for human
consumption and gives LF (or NUL when -z is used) the "separator"
semantics, i.e. when listing things A B and C, we would throw
separator in between but not before the first one (obviously) and
not after the last one.  "--format=..." which is a synonym for
"--pretty=tformat:..." is designed for tool consumption and gives LF
(or NULL when -z i used) the "terminator" semantics, i.e. each item
in the output is followed by terminator, so in addition to LF/NUL
after A and B in the example in this paragraph, you also get one
after C, which is the last item.