Can a Git hook automatically add files to the commit?

Question

I'd like to add an automatically generated file to the same commit using a pre- or post-commit hook in Git, dependent on the files that were modified in that commit. How would I go about this?

I've tried this as a pre-commit hook, but no luck:

#!/bin/sh
files=`git diff --cached --name-status`
re="<files of importance>"
if [[ $files =~ $re ]]
then
  echo "Creating files"
  exec bundle exec create_my_files
  exec git add my_files
  exec git commit --amend -C HEAD
fi

This successfully adds them to the repository, but does not add them to the commit. I've also tried using the last two exec lines in a post-commit hook along with the pre-commit inspection, but no good either.

Answer 1

Since git add was also not working for me in a pre commit, I followed mark's idea of using a .commit file and splitting the process into pre- and post-commit.

Here is some code that should be easy to understand

In the pre-commit:

• Touch a file .commit or something. (be sure to add this to .gitignore)

#!/bin/sh 
echo 
touch .commit 
exit

In the post-commit:

if .commit exists you know a commit has just taken place but a post-commit hasn't run yet. So, you can do your code generation here. Additionally, test for .commit and if it exists:

• add the files
• commit --amend -C HEAD --no-verify (avoid looping)
• delete .commit file

#!/bin/sh
echo
if [ -e .commit ]
    then
    rm .commit
    git add yourfile
    git commit --amend -C HEAD --no-verify
fi
exit

Hope this makes it easier for people with few bash knowledge to follow mark's idea.

Answer 2

It's possible to do what you want using pre-commit hooks. We do something similar for a heroku deployment (compiling coffeescript to javascript). The reason your script isn't working is because you used the exec command improperly.

From the man page:

The exec builtin is used to replace the currently running shells process image with a new command. On successful completion, exec never returns. exec can not be used inside a pipeline.

Only your first exec command is running. After that your script is basically terminated.

Give something like this a try (as a pre-commit hook):

#!/bin/sh
files=`git diff --cached --name-status`
re="<files of importance>"
if [[ $files =~ $re ]]
then
  echo "Creating files"
  bundle exec create_my_files
  git add my_files
fi

Answer 3

#!/bin/sh
#
#  .git/hooks/pre-commit
#

git add file.xyz

This worked just fine for me. It will be part of the current commit.

git version 1.7.12.4 (Apple Git-37)

Answer 4

You could use a combination of a pre and post commit script.

In the pre-commit:

• Touch a file .commit or something. (be sure to add this to .gitignore)

In the post-commit:

if .commit exists you know a commit has just taken place but a post-commit hasn't run yet. So, you can do your code generation here. Additionally, test for .commit and if it exists:

• add the files
• commit --amend -C HEAD --no-verify (avoid looping)
• delete .commit file

This is roughly the process I use to store a .metadata file in the repository generated from metastore.

If anyone knows a better way I'm all ears but it seems to work for now.

Answer 5

You can use update-index:

git update-index --add my_files

Answer 6

How about writing a post-commit script instead which generates your files, and then have that do (something along the lines of) git add my_files; git commit --amend.

Answer 7

I had the same need and this approach worked pretty well for me:

#!/bin/sh
files='git diff --cached --name-only'
re="<files of importance>"
if [[ $files =~ $re ]]
then
   echo "Creating files"
   create_my_files && git add my_files
fi

where "create_my_files" should be executable, for example if it is a python file you could execute it as "python create_my_files && git add my_files"

and is true you don't need a pre-commit to commit again (that would create a infinite nasty loop :p)

Answer 8

If the files are automatically generated, and they can be generated anywhere (implicit in your desire to build them in the Git pre-commit hook) then you shouldn't be putting them under source control in the first place. You should only control source files -- generated files should be generated as part of the build scripts.

The only reason to put a generated file under source control is when it requires unique/privileged resources to generate (such as a licensed program) or it requires a significant amount of time to generate.

Added

From http://git-scm.com/docs/githooks :

pre-commit This hook is invoked by git commit, and can be bypassed with --no-verify option. It takes no parameter, and is invoked before obtaining the proposed commit log message and making a commit. Exiting with non-zero status from this script causes the git commit to abort.

The default pre-commit hook, when enabled, catches introduction of lines with trailing whitespaces and aborts the commit when such a line is found.

All the git commit hooks are invoked with the environment variable GIT_EDITOR=: if the command will not bring up an editor to modify the commit message.

The intent of the pre-commit hook is to be a pass-fail check on the state of the workspace and the contents of the commit, prior to making the commit. Attempting to change the contents of the commit won't work.

My recommendation would be add two steps to your build scripts: (1) a step that will build all of the out-of-date files that needs to be generated (and adds them to the workspace), and (2) a step that will check to ensure that all of the generated files are up-to-date, and return a non-zero status code. Your Git pre-commit hook should run the second step. Your developers should be trained to run the first step as necessary.

Answer 9

Yes, you can add generated files automatically on the commit using git hooks! But it requires a tricky script.

Here you can find the problem solved. There, it is updating the file version on every commit, adding a new modified file and amending the commit as you need it to. It is fully working: https://github.com/evandrocoan/.versioning

Then you just replace the 'Version File Replacement' algorithm on the file 'updateVersion.sh', by your algorithm. Maybe you need to change a few things like, remove the branch limitation, because there, the script only runs if you are on the 'develop' branch.

Also, it will only change the specified file, if is staged. If the file is not staged, then it will do nothing than the normal/usual commit. More precisely, it print out what it is doing on every step.

I am going to explain, that trick. It is quite tricky. On the prepare-commit-msg-hook, it detects whether the desired file is being staged and committed. After that, it creates a flag file, and stops the prepare-commit-msg-hook. Later on the post-commit-hook, it checks whether the flag file exists. If yes, it amends the files on the commit.

Attention, it would create a infinity loop because it would call again the prepare-commit-msg-hook (as we are amending). But it does not happen because of the flag file. When the prepare-commit-msg-hook runs and find the flag file, it "knows" what is happening. Then is just deletes the flag file and do not create it again. Doing it, it will block the post-commit-hook from amending again the commits, allowing the commit to finish for good.

Answer 10

I was facing same problem in pre-commit hook also. I was modifying one file and committing but it was taking previous file not updated file so by adding git command(as below) in pre-commit hook, it solved.

git add $file

note: $file is your file to be added.