How to include the current Git commit ID and branch in my document?

Question

I use Git to track changes on my TEX files. When producing a PDF, it would be nice to include the current branch and commit ID somewhere in the document (e.g. on the title page or in a footer).

I know that the package gitinfo2 exists but I'd rather avoid adding any hooks to Git. Besides, I am aware of this question but I would prefer a solution that does not require enabling write18.

Given that the name of the current branch can be found in .git/HEAD and the current commit ID is stored in .git/refs/heads/[name of branch], is it possible to embed this information in the final document?

CL. · Accepted Answer

As stated in the question, the branch name can be extracted from .git/HEAD and given [branch name], the commit ID can be found in .git/refs/heads/[branch name].
The package catchfile provides the command CatchFileDef, which allows us to read .git/HEAD into a macro. As HEAD has no file extension, MiKTeX users have to add a trailing dot to the file name:
CatchFileDef{headfull}{.git/HEAD.}{}

This assigns something like ref: refs/heads/master  to headfull. As this string has a trailing whitespace character, we use StrGobbleRight from the xstring package to trim it:1
StrGobbleRight{headfull}{1}[head]

In order to extract only the branch name (master in the example) from this string, we can use StrBehind:
StrBehind[2]{head}{/}[branch]

This saves the branch name in branch. Finally, we can use CatchFileDef again, to save the commit ID in commit:
CatchFileDef{commit}{.git/refs/heads/branch.}{}

There are some edge cases where .git/refs/heads/branch. does not exist: After running git pack-refs (which is a side effect of git gc --aggressive, for example), the heads are packed into the file .git/packed-refs instead of individual branchname files. As a workaround, check if the file exists before trying to read it:
IfFileExists{.git/refs/heads/branch.}{%
    CatchFileDef{commit}{.git/refs/heads/branch.}{}}{%
    newcommand{commit}{dots~(in emph{packed-refs})}}

As a fallback, this creates the (not-so-useful) output "... (in packed-refs)" instead of a commit ID – but this only lasts until the next commit, when the file heads/branchname is recreated for the affected branch.
(A more ambitious workaround could parse packed-refs, of course.)
Full MWE:
documentclass{article}

usepackage{xstring}
usepackage{catchfile}

CatchFileDef{headfull}{.git/HEAD.}{}
StrGobbleRight{headfull}{1}[head]
StrBehind[2]{head}{/}[branch]
IfFileExists{.git/refs/heads/branch.}{%
    CatchFileDef{commit}{.git/refs/heads/branch.}{}}{%
    newcommand{commit}{dots~(in emph{packed-refs})}}

begin{document}
This revision: texttt{commit} on branch texttt{branch}.
end{document}

Sample output:

This revision: d92dc1386e48e04ceecb85461ed3b232146e6a32 on branch
master.

1 Using the last optional argument of StrGobbleRight (name) to assign the trimmed string to a macro (head) is necessary to allow further manipulation of the string using the xstring functions – see here for a discussion.

user4686 · Answer

A no-package approach (tested on mac os, modify it for Windows regarding extra needed dot perhaps) based on @CL.'s answer.
documentclass{article}

newcommanddotGitHEAD{}
newcommandbranch{}
newcommandcommit{}

makeatletterletmyfilehandle@inputcheckmakeatother

openinmyfilehandle=.git/HEADrelax

begingroupendlinechar-1
  globalreadmyfilehandle to dotGitHEAD
endgroup
closeinmyfilehandle

newcommandGetBranch{}
defGetBranch ref: refs/heads/#1relax{renewcommand{branch}{#1}}

expandafterGetBranchdotGitHEADrelax

openinmyfilehandle=.git/refs/heads/branchrelax

begingroupendlinechar-1
  globalreadmyfilehandle to commit
endgroup
closeinmyfilehandle

begin{document}
branch+++

commit+++

This revision: texttt{commit} on branch texttt{branch}.
end{document}

Package getcommit:
ProvidesPackage{getcommit}[2018/10/16 get current commit and branch (JFB)]

@ifundefined{branch}{}
   {PackageWarning{getcommit}{ATTENTION!^^J
    @spaces@spacesstringbranchspace macro was already
    defined. Overwritten.}}
@ifundefined{commit}{}
   {PackageWarning{getcommit}{ATTENTION!^^J
    @spaces@spacesstringcommitspace macro was already
    defined. Overwritten.}}

openin@inputcheck=.git/HEADrelax

begingroupendlinechar-1
  globalread@inputcheck to getcommit@HEAD
endgroup
closein@inputcheck

defgetcommit@GetBranch ref: refs/heads/#1relax{defbranch{#1}}

expandaftergetcommit@GetBranchgetcommit@HEADrelax

openin@inputcheck=.git/refs/heads/branchrelax

begingroupendlinechar-1
  globalread@inputcheck to commit
endgroup
closein@inputcheck
endinput

Example of use:
documentclass{article}

usepackage{getcommit}

begin{document}
+++branch+++

+++commit+++

%frenchspacing
This revision: texttt{commit} on branch texttt{branch}.
end{document}

wipet · Answer

We can use input instead read primitive:
defgitdir{.git/}
defreadgitcommitA #1 {defgitcommit{#1}}
defreadgitbranchA #1 #2 {defgitbranch{#2}}
defreadgitcommit{expandafterreadgitbranchA input gitdir HEAD
  expandafterreadgitcommitA input gitdirgitbranchrelax}

readgitcommit

Now, the commit ID is in "gitcommit" macro.

canochordo · Answer

If you are using latexmk,
you can use an alternative approach to intialize gitinfo2,
that does not require git hooks (https://github.com/rbarazzutti/gitinfo2-latexmk).
Setup:
$ git submodule add https://github.com/rbarazzutti/gitinfo2-latexmk gitinfo2-latexmk
$ echo "do './gitinfo2-latexmk/gitinfo2.pm';" >> latexmkrc

Usage:
usepackage[mark]{gitinfo2}

How to include the current Git commit ID and branch in my document?

4 Answers

Full MWE:

Sample output:

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