Git Filter-Branch

Git's git filter-branch command is a powerful and flexible tool for rewriting Git history. Whether you need to filter out sensitive information, reorganize commits, or split a repository, git filter-branch empowers you to shape your project's history. We'll explore various ways to use the git filter-branch command, providing you with a comprehensive guide to manipulating Git history.

1. Basic Syntax:

The basic syntax of git filter-branch is as follows:

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git filter-branch <options> <commit-range>

Replace <options> with the specific filters or actions you want to apply and <commit-range> with the range of commits you want to process.

2. Removing a File from History:

To remove a specific file from Git history, use the --index-filter option:

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git filter-branch --index-filter 'git rm --cached --ignore-unmatch <file>' HEAD

Replace <file> with the path to the file you want to remove.

3. Filtering Commits Based on Commit Message:

You can filter commits based on commit messages using the --commit-filter option. For example, to keep only commits containing a specific keyword:

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git filter-branch --commit-filter 'if  "$(git log --format=%B -n 1 "$GIT_COMMIT" | grep "keyword")" ; then git commit-tree -u "$GIT_AUTHOR_EMAIL" -m "$GIT_COMMIT"; else skip_commit "$@"; fi' HEAD

Replace "keyword" with the keyword you want to filter by.

4. Removing Files Matching a Pattern:

To remove files matching a specific pattern from history, use the --tree-filter option:

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git filter-branch --tree-filter 'find . -type f -name "*.log" -exec rm -f {} \;' HEAD

This example removes all files with a .log extension.

5. Removing Empty Commits:

To remove empty commits from history, use the --prune-empty option:

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git filter-branch --prune-empty HEAD

This removes commits that don't introduce changes.

6. Changing Author Information:

To change author information, use the --env-filter option. For example, to update the email address:

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git filter-branch --env-filter 'if  "$GIT_AUTHOR_EMAIL" = "[email protected]" ; then export GIT_AUTHOR_EMAIL="[email protected]"; fi' HEAD

Replace "[email protected]" and "[email protected]" with the old and new email addresses, respectively.

7. Combining Multiple Filters:

You can combine multiple filters in a single git filter-branch command. For instance, to remove a file and change author information:

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git filter-branch --index-filter 'git rm --cached --ignore-unmatch <file>' --env-filter 'if  "$GIT_AUTHOR_EMAIL" = "[email protected]" ; then export GIT_AUTHOR_EMAIL="[email protected]"; fi' HEAD

Replace <file> with the path to the file you want to remove.

8. Splitting a Repository:

To split a repository into multiple repositories, use the --subdirectory-filter option:

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git filter-branch --subdirectory-filter <subdirectory> -- --all

Replace <subdirectory> with the path to the subdirectory you want to extract.

9. Limiting the Range of Commits:

You can limit the range of commits to be processed using commit hashes. For example, to process only commits between commitA and commitB:

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git filter-branch <options> commitA^..commitB

Replace <options> with the desired filters.

10. Keeping Only Specific Branch:

To keep only a specific branch and remove other branches, use the refs/heads/<branch> specification:

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git filter-branch --tag-name-filter cat -- --all

Replace <branch> with the name of the branch you want to keep.

11. Preserving Tags:

When filtering branches, tags are not preserved by default. To preserve tags, use the --tag-name-filter option:

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git filter-branch --tag-name-filter cat -- --all

12. Cleaning Up Reflog and Garbage Collection:

After using git filter-branch, clean up the reflog and perform garbage collection to optimize the repository:

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git reflog expire --expire=now --all
git gc --prune=now