Prior to that, the $GIT_COMMIT environment variable will be set to contain
the id of the commit being rewritten. Also, GIT_AUTHOR_NAME,
GIT_AUTHOR_EMAIL, GIT_AUTHOR_DATE, GIT_COMMITTER_NAME, GIT_COMMITTER_EMAIL,
-and GIT_COMMITTER_DATE are set according to the current commit. The values
-of these variables after the filters have run, are used for the new commit.
+and GIT_COMMITTER_DATE are taken from the current commit and exported to
+the environment, in order to affect the author and committer identities of
+the replacement commit created by linkgit:git-commit-tree[1] after the
+filters have run.
+
If any evaluation of <command> returns a non-zero exit status, the whole
operation will be aborted.
' HEAD~10..HEAD
--------------------------------------------------------
+The `--env-filter` option can be used to modify committer and/or author
+identity. For example, if you found out that your commits have the wrong
+identity due to a misconfigured user.email, you can make a correction,
+before publishing the project, like this:
+
+--------------------------------------------------------
+git filter-branch --env-filter '
+ if test "$GIT_AUTHOR_EMAIL" = "root@localhost"
+ then
+ GIT_AUTHOR_EMAIL=john@example.com
+ export GIT_AUTHOR_EMAIL
+ fi
+ if test "$GIT_COMMITTER_EMAIL" = "root@localhost"
+ then
+ GIT_COMMITTER_EMAIL=john@example.com
+ export GIT_COMMITTER_EMAIL
+ fi
+' -- --all
+--------------------------------------------------------
+
To restrict rewriting to only part of the history, specify a revision
range in addition to the new branch name. The new branch name will
point to the top-most revision that a 'git rev-list' of this range
Checklist for Shrinking a Repository
------------------------------------
-git-filter-branch is often used to get rid of a subset of files,
+git-filter-branch can be used to get rid of a subset of files,
usually with some combination of `--index-filter` and
`--subdirectory-filter`. People expect the resulting repository to
be smaller than the original, but you need a few more steps to
(or if your git-gc is not new enough to support arguments to
`--prune`, use `git repack -ad; git prune` instead).
+Notes
+-----
+
+git-filter-branch allows you to make complex shell-scripted rewrites
+of your Git history, but you probably don't need this flexibility if
+you're simply _removing unwanted data_ like large files or passwords.
+For those operations you may want to consider
+link:http://rtyley.github.io/bfg-repo-cleaner/[The BFG Repo-Cleaner],
+a JVM-based alternative to git-filter-branch, typically at least
+10-50x faster for those use-cases, and with quite different
+characteristics:
+
+* Any particular version of a file is cleaned exactly _once_. The BFG,
+ unlike git-filter-branch, does not give you the opportunity to
+ handle a file differently based on where or when it was committed
+ within your history. This constraint gives the core performance
+ benefit of The BFG, and is well-suited to the task of cleansing bad
+ data - you don't care _where_ the bad data is, you just want it
+ _gone_.
+
+* By default The BFG takes full advantage of multi-core machines,
+ cleansing commit file-trees in parallel. git-filter-branch cleans
+ commits sequentially (ie in a single-threaded manner), though it
+ _is_ possible to write filters that include their own parallellism,
+ in the scripts executed against each commit.
+
+* The link:http://rtyley.github.io/bfg-repo-cleaner/#examples[command options]
+ are much more restrictive than git-filter branch, and dedicated just
+ to the tasks of removing unwanted data- e.g:
+ `--strip-blobs-bigger-than 1M`.
+
GIT
---
Part of the linkgit:git[1] suite