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

Imagine you have a pre-commit hook that does this:

#!/bin/bash

echo "--- Dataset Pre-Commit Hook ---"

DATASET_REPO_PATH="$(pwd)"

python3 -m my_script_that_generates_or_modifies_a_file
git -C $DATASET_REPO_PATH add file

echo "--- Done ---"
exit

It will work IF AND ONLY IF, there was already something to be commited. It does not have to be the same file tho. If there was nothing to be commited, the git add git add file will work, but will not be commited.

Example that works:

1. You changed a file, and added it (for example, the gitignore)

$> git status
On branch master

No commits yet

Changes to be committed:
  (use "git rm --cached <file>..." to unstage)
        new file:   .gitignore

2. Run commit. First, the pre-commit hook will run and create file. Then it will commit.

--- Dataset Pre-Commit Hook ---
--- Done ---
[master (root-commit) 2ba2f7c] First commit
 3 files changed, 34 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 file

3. You can see the message says file was commited. And git status now outputs:

On branch master
nothing to commit, working tree clean

Example that DOES NOT work

1. You have nothing to add. You can of course run git add but it will do nothing. git status gives:

On branch master
Your branch is up to date with 'origin/master'.

nothing to commit, working tree clean

2. Run commit. The hook will create file. But the commit message says he did nothing.

--- Dataset Pre-Commit Hook ---
--- Done ---
On branch master
Your branch is up to date with 'origin/master'.

nothing to commit, working tree clean

3. Verify the status git status

On branch master
Your branch is up to date with 'origin/master'.

Changes to be committed:
  (use "git restore --staged <file>..." to unstage)
        modified:   file

3. You can see that file was indeed modified, and that it was added, but yet not commited. You need to run git commit again for it to work.

I tried adding that as a post-commit hook but got no luck. If someone knows a fix for this case, I would love to know.

Answer 2

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.

Answer 3

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 4

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 5

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 6

You can use update-index:

git update-index --add my_files

Answer 7

#!/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 8

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 9

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 10

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 11

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.