GIT-REBASE(1) - phpMan

GIT-REBASE(1) Git Manual GIT-REBASE(1)

NAME
git-rebase - Forward-port local commits to the updated upstream head

DESCRIPTION
If <branch> is specified, git rebase will perform an automatic git checkout <branch>
before doing anything else. Otherwise it remains on the current branch.

If <upstream> is not specified, the upstream configured in branch.<name>.remote and
branch.<name>.merge options will be used; see git-config(1) for details. If you are
currently not on any branch or if the current branch does not have a configured upstream,
the rebase will abort.

All changes made by commits in the current branch but that are not in <upstream> are saved
to a temporary area. This is the same set of commits that would be shown by git log
<upstream>..HEAD (or git log HEAD, if --root is specified).

The current branch is reset to <upstream>, or <newbase> if the --onto option was supplied.
This has the exact same effect as git reset --hard <upstream> (or <newbase>). ORIG_HEAD is
set to point at the tip of the branch before the reset.

The commits that were previously saved into the temporary area are then reapplied to the
current branch, one by one, in order. Note that any commits in HEAD which introduce the
same textual changes as a commit in HEAD..<upstream> are omitted (i.e., a patch already
accepted upstream with a different commit message or timestamp will be skipped).

It is possible that a merge failure will prevent this process from being completely
automatic. You will have to resolve any such merge failure and run git rebase --continue.
Another option is to bypass the commit that caused the merge failure with git rebase
--skip. To check out the original <branch> and remove the .git/rebase-apply working files,
use the command git rebase --abort instead.

Assume the following history exists and the current branch is "topic":

A---B---C topic
/
D---E---F---G master

From this point, the result of either of the following commands:

git rebase master
git rebase master topic

would be:

A'--B'--C' topic
/
D---E---F---G master

NOTE: The latter form is just a short-hand of git checkout topic followed by git rebase
master. When rebase exits topic will remain the checked-out branch.

If the upstream branch already contains a change you have made (e.g., because you mailed a
patch which was applied upstream), then that commit will be skipped. For example, running
`git rebase master` on the following history (in which A' and A introduce the same set of
changes, but have different committer information):

A---B---C topic
/
D---E---A'---F master

will result in:

B'---C' topic
/
D---E---A'---F master

Here is how you would transplant a topic branch based on one branch to another, to pretend
that you forked the topic branch from the latter branch, using rebase --onto.

First let's assume your topic is based on branch next. For example, a feature developed in
topic depends on some functionality which is found in next.

o---o---o---o---o master
\
o---o---o---o---o next
\
o---o---o topic

We want to make topic forked from branch master; for example, because the functionality on
which topic depends was merged into the more stable master branch. We want our tree to
look like this:

o---o---o---o---o master
| \
| o'--o'--o' topic
\
o---o---o---o---o next

We can get this using the following command:

git rebase --onto master next topic

Another example of --onto option is to rebase part of a branch. If we have the following
situation:

H---I---J topicB
/
E---F---G topicA
/
A---B---C---D master

then the command

git rebase --onto master topicA topicB

would result in:

H'--I'--J' topicB
/
| E---F---G topicA
|/
A---B---C---D master

This is useful when topicB does not depend on topicA.

A range of commits could also be removed with rebase. If we have the following situation:

E---F---G---H---I---J topicA

then the command

git rebase --onto topicA~5 topicA~3 topicA

would result in the removal of commits F and G:

E---H'---I'---J' topicA

This is useful if F and G were flawed in some way, or should not be part of topicA. Note
that the argument to --onto and the <upstream> parameter can be any valid commit-ish.

In case of conflict, git rebase will stop at the first problematic commit and leave
conflict markers in the tree. You can use git diff to locate the markers (<<<<<<) and make
edits to resolve the conflict. For each file you edit, you need to tell Git that the
conflict has been resolved, typically this would be done with

git add <filename>

After resolving the conflict manually and updating the index with the desired resolution,
you can continue the rebasing process with

git rebase --continue

Alternatively, you can undo the git rebase with

git rebase --abort

CONFIGURATION
rebase.stat
Whether to show a diffstat of what changed upstream since the last rebase. False by
default.

rebase.autosquash
If set to true enable --autosquash option by default.

OPTIONS
--onto <newbase>
Starting point at which to create the new commits. If the --onto option is not
specified, the starting point is <upstream>. May be any valid commit, and not just an
existing branch name.

As a special case, you may use "A...B" as a shortcut for the merge base of A and B if
there is exactly one merge base. You can leave out at most one of A and B, in which
case it defaults to HEAD.

<upstream>
Upstream branch to compare against. May be any valid commit, not just an existing
branch name. Defaults to the configured upstream for the current branch.

<branch>
Working branch; defaults to HEAD.

--continue
Restart the rebasing process after having resolved a merge conflict.

--abort
Abort the rebase operation and reset HEAD to the original branch. If <branch> was
provided when the rebase operation was started, then HEAD will be reset to <branch>.
Otherwise HEAD will be reset to where it was when the rebase operation was started.

--keep-empty
Keep the commits that do not change anything from its parents in the result.

--skip
Restart the rebasing process by skipping the current patch.

--edit-todo
Edit the todo list during an interactive rebase.

-m, --merge
Use merging strategies to rebase. When the recursive (default) merge strategy is used,
this allows rebase to be aware of renames on the upstream side.

Note that a rebase merge works by replaying each commit from the working branch on top
of the <upstream> branch. Because of this, when a merge conflict happens, the side
reported as ours is the so-far rebased series, starting with <upstream>, and theirs is
the working branch. In other words, the sides are swapped.

-s <strategy>, --strategy=<strategy>
Use the given merge strategy. If there is no -s option git merge-recursive is used
instead. This implies --merge.

Because git rebase replays each commit from the working branch on top of the
<upstream> branch using the given strategy, using the ours strategy simply discards
all patches from the <branch>, which makes little sense.

-X <strategy-option>, --strategy-option=<strategy-option>
Pass the <strategy-option> through to the merge strategy. This implies --merge and, if
no strategy has been specified, -s recursive. Note the reversal of ours and theirs as
noted above for the -m option.

-q, --quiet
Be quiet. Implies --no-stat.

-v, --verbose
Be verbose. Implies --stat.

--stat
Show a diffstat of what changed upstream since the last rebase. The diffstat is also
controlled by the configuration option rebase.stat.

-n, --no-stat
Do not show a diffstat as part of the rebase process.

--no-verify
This option bypasses the pre-rebase hook. See also githooks(5).

--verify
Allows the pre-rebase hook to run, which is the default. This option can be used to
override --no-verify. See also githooks(5).

-C<n>
Ensure at least <n> lines of surrounding context match before and after each change.
When fewer lines of surrounding context exist they all must match. By default no
context is ever ignored.

-f, --force-rebase
Force the rebase even if the current branch is a descendant of the commit you are
rebasing onto. Normally non-interactive rebase will exit with the message "Current
branch is up to date" in such a situation. Incompatible with the --interactive option.

You may find this (or --no-ff with an interactive rebase) helpful after reverting a
topic branch merge, as this option recreates the topic branch with fresh commits so it
can be remerged successfully without needing to "revert the reversion" (see the
revert-a-faulty-merge How-To[1] for details).

--ignore-whitespace, --whitespace=<option>
These flag are passed to the git apply program (see git-apply(1)) that applies the
patch. Incompatible with the --interactive option.

--committer-date-is-author-date, --ignore-date
These flags are passed to git am to easily change the dates of the rebased commits
(see git-am(1)). Incompatible with the --interactive option.

-i, --interactive
Make a list of the commits which are about to be rebased. Let the user edit that list
before rebasing. This mode can also be used to split commits (see SPLITTING COMMITS
below).

-p, --preserve-merges
Instead of ignoring merges, try to recreate them.

This uses the --interactive machinery internally, but combining it with the
--interactive option explicitly is generally not a good idea unless you know what you
are doing (see BUGS below).

-x <cmd>, --exec <cmd>
Append "exec <cmd>" after each line creating a commit in the final history. <cmd> will
be interpreted as one or more shell commands.

This option can only be used with the --interactive option (see INTERACTIVE MODE
below).

You may execute several commands by either using one instance of --exec with several
commands:

git rebase -i --exec "cmd1 && cmd2 && ..."

or by giving more than one --exec:

git rebase -i --exec "cmd1" --exec "cmd2" --exec ...

If --autosquash is used, "exec" lines will not be appended for the intermediate
commits, and will only appear at the end of each squash/fixup series.

--root
Rebase all commits reachable from <branch>, instead of limiting them with an
<upstream>. This allows you to rebase the root commit(s) on a branch. When used with
--onto, it will skip changes already contained in <newbase> (instead of <upstream>)
whereas without --onto it will operate on every change. When used together with both
--onto and --preserve-merges, all root commits will be rewritten to have <newbase> as
parent instead.

--autosquash, --no-autosquash
When the commit log message begins with "squash! ..." (or "fixup! ..."), and there is
a commit whose title begins with the same ..., automatically modify the todo list of
rebase -i so that the commit marked for squashing comes right after the commit to be
modified, and change the action of the moved commit from pick to squash (or fixup).

This option is only valid when the --interactive option is used.

If the --autosquash option is enabled by default using the configuration variable
rebase.autosquash, this option can be used to override and disable this setting.

--no-ff
With --interactive, cherry-pick all rebased commits instead of fast-forwarding over
the unchanged ones. This ensures that the entire history of the rebased branch is
composed of new commits.

Without --interactive, this is a synonym for --force-rebase.

You may find this helpful after reverting a topic branch merge, as this option
recreates the topic branch with fresh commits so it can be remerged successfully
without needing to "revert the reversion" (see the revert-a-faulty-merge How-To[1] for
details).

MERGE STRATEGIES
The merge mechanism (git-merge and git-pull commands) allows the backend merge strategies
to be chosen with -s option. Some strategies can also take their own options, which can be
passed by giving -X<option> arguments to git-merge and/or git-pull.

resolve
This can only resolve two heads (i.e. the current branch and another branch you pulled
from) using a 3-way merge algorithm. It tries to carefully detect criss-cross merge
ambiguities and is considered generally safe and fast.

recursive
This can only resolve two heads using a 3-way merge algorithm. When there is more than
one common ancestor that can be used for 3-way merge, it creates a merged tree of the
common ancestors and uses that as the reference tree for the 3-way merge. This has
been reported to result in fewer merge conflicts without causing mis-merges by tests
done on actual merge commits taken from Linux 2.6 kernel development history.
Additionally this can detect and handle merges involving renames. This is the default
merge strategy when pulling or merging one branch.

The recursive strategy can take the following options:

ours
This option forces conflicting hunks to be auto-resolved cleanly by favoring our
version. Changes from the other tree that do not conflict with our side are
reflected to the merge result. For a binary file, the entire contents are taken
from our side.

This should not be confused with the ours merge strategy, which does not even look
at what the other tree contains at all. It discards everything the other tree did,
declaring our history contains all that happened in it.

theirs
This is the opposite of ours.

patience
With this option, merge-recursive spends a little extra time to avoid mismerges
that sometimes occur due to unimportant matching lines (e.g., braces from distinct
functions). Use this when the branches to be merged have diverged wildly. See also
git-diff(1)--patience.

diff-algorithm=[patience|minimal|histogram|myers]
Tells merge-recursive to use a different diff algorithm, which can help avoid
mismerges that occur due to unimportant matching lines (such as braces from
distinct functions). See also git-diff(1)--diff-algorithm.

ignore-space-change, ignore-all-space, ignore-space-at-eol
Treats lines with the indicated type of whitespace change as unchanged for the
sake of a three-way merge. Whitespace changes mixed with other changes to a line
are not ignored. See also git-diff(1)-b, -w, and --ignore-space-at-eol.

o If their version only introduces whitespace changes to a line, our version is
used;

o If our version introduces whitespace changes but their version includes a
substantial change, their version is used;

o Otherwise, the merge proceeds in the usual way.

renormalize
This runs a virtual check-out and check-in of all three stages of a file when
resolving a three-way merge. This option is meant to be used when merging branches
with different clean filters or end-of-line normalization rules. See "Merging
branches with differing checkin/checkout attributes" in gitattributes(5) for
details.

no-renormalize
Disables the renormalize option. This overrides the merge.renormalize
configuration variable.

rename-threshold=<n>
Controls the similarity threshold used for rename detection. See also git-
diff(1)-M.

subtree[=<path>]
This option is a more advanced form of subtree strategy, where the strategy makes
a guess on how two trees must be shifted to match with each other when merging.
Instead, the specified path is prefixed (or stripped from the beginning) to make
the shape of two trees to match.

octopus
This resolves cases with more than two heads, but refuses to do a complex merge that
needs manual resolution. It is primarily meant to be used for bundling topic branch
heads together. This is the default merge strategy when pulling or merging more than
one branch.

ours
This resolves any number of heads, but the resulting tree of the merge is always that
of the current branch head, effectively ignoring all changes from all other branches.
It is meant to be used to supersede old development history of side branches. Note
that this is different from the -Xours option to the recursive merge strategy.

subtree
This is a modified recursive strategy. When merging trees A and B, if B corresponds to
a subtree of A, B is first adjusted to match the tree structure of A, instead of
reading the trees at the same level. This adjustment is also done to the common
ancestor tree.

NOTES
You should understand the implications of using git rebase on a repository that you share.
See also RECOVERING FROM UPSTREAM REBASE below.

When the git-rebase command is run, it will first execute a "pre-rebase" hook if one
exists. You can use this hook to do sanity checks and reject the rebase if it isn't
appropriate. Please see the template pre-rebase hook script for an example.

Upon completion, <branch> will be the current branch.

INTERACTIVE MODE
Rebasing interactively means that you have a chance to edit the commits which are rebased.
You can reorder the commits, and you can remove them (weeding out bad or otherwise
unwanted patches).

The interactive mode is meant for this type of workflow:

1. have a wonderful idea

2. hack on the code

3. prepare a series for submission

4. submit

where point 2. consists of several instances of

a) regular use

1. finish something worthy of a commit

2. commit

b) independent fixup

1. realize that something does not work

2. fix that

3. commit it

Sometimes the thing fixed in b.2. cannot be amended to the not-quite perfect commit it
fixes, because that commit is buried deeply in a patch series. That is exactly what
interactive rebase is for: use it after plenty of "a"s and "b"s, by rearranging and
editing commits, and squashing multiple commits into one.

Start it with the last commit you want to retain as-is:

git rebase -i <after-this-commit>

An editor will be fired up with all the commits in your current branch (ignoring merge
commits), which come after the given commit. You can reorder the commits in this list to
your heart's content, and you can remove them. The list looks more or less like this:

pick deadbee The oneline of this commit
pick fa1afe1 The oneline of the next commit
...

The oneline descriptions are purely for your pleasure; git rebase will not look at them
but at the commit names ("deadbee" and "fa1afe1" in this example), so do not delete or
edit the names.

By replacing the command "pick" with the command "edit", you can tell git rebase to stop
after applying that commit, so that you can edit the files and/or the commit message,
amend the commit, and continue rebasing.

If you just want to edit the commit message for a commit, replace the command "pick" with
the command "reword".

If you want to fold two or more commits into one, replace the command "pick" for the
second and subsequent commits with "squash" or "fixup". If the commits had different
authors, the folded commit will be attributed to the author of the first commit. The
suggested commit message for the folded commit is the concatenation of the commit messages
of the first commit and of those with the "squash" command, but omits the commit messages
of commits with the "fixup" command.

git rebase will stop when "pick" has been replaced with "edit" or when a command fails due
to merge errors. When you are done editing and/or resolving conflicts you can continue
with git rebase --continue.

For example, if you want to reorder the last 5 commits, such that what was HEAD~4 becomes
the new HEAD. To achieve that, you would call git rebase like this:

$ git rebase -i HEAD~5

And move the first patch to the end of the list.

You might want to preserve merges, if you have a history like this:

X
\
A---M---B
/
---o---O---P---Q

Suppose you want to rebase the side branch starting at "A" to "Q". Make sure that the
current HEAD is "B", and call

$ git rebase -i -p --onto Q O

Reordering and editing commits usually creates untested intermediate steps. You may want
to check that your history editing did not break anything by running a test, or at least
recompiling at intermediate points in history by using the "exec" command (shortcut "x").
You may do so by creating a todo list like this one:

pick deadbee Implement feature XXX
fixup f1a5c00 Fix to feature XXX
exec make
pick c0ffeee The oneline of the next commit
edit deadbab The oneline of the commit after
exec cd subdir; make test
...

The interactive rebase will stop when a command fails (i.e. exits with non-0 status) to
give you an opportunity to fix the problem. You can continue with git rebase --continue.

The "exec" command launches the command in a shell (the one specified in $SHELL, or the
default shell if $SHELL is not set), so you can use shell features (like "cd", ">", ";"
...). The command is run from the root of the working tree.

$ git rebase -i --exec "make test"

This command lets you check that intermediate commits are compilable. The todo list
becomes like that:

pick 5928aea one
exec make test
pick 04d0fda two
exec make test
pick ba46169 three
exec make test
pick f4593f9 four
exec make test

SPLITTING COMMITS
In interactive mode, you can mark commits with the action "edit". However, this does not
necessarily mean that git rebase expects the result of this edit to be exactly one commit.
Indeed, you can undo the commit, or you can add other commits. This can be used to split a
commit into two:

o Start an interactive rebase with git rebase -i <commit>^, where <commit> is the commit
you want to split. In fact, any commit range will do, as long as it contains that
commit.

o Mark the commit you want to split with the action "edit".

o When it comes to editing that commit, execute git reset HEAD^. The effect is that the
HEAD is rewound by one, and the index follows suit. However, the working tree stays
the same.

o Now add the changes to the index that you want to have in the first commit. You can
use git add (possibly interactively) or git gui (or both) to do that.

o Commit the now-current index with whatever commit message is appropriate now.

o Repeat the last two steps until your working tree is clean.

o Continue the rebase with git rebase --continue.

If you are not absolutely sure that the intermediate revisions are consistent (they
compile, pass the testsuite, etc.) you should use git stash to stash away the
not-yet-committed changes after each commit, test, and amend the commit if fixes are
necessary.

RECOVERING FROM UPSTREAM REBASE
Rebasing (or any other form of rewriting) a branch that others have based work on is a bad
idea: anyone downstream of it is forced to manually fix their history. This section
explains how to do the fix from the downstream's point of view. The real fix, however,
would be to avoid rebasing the upstream in the first place.

To illustrate, suppose you are in a situation where someone develops a subsystem branch,
and you are working on a topic that is dependent on this subsystem. You might end up with
a history like the following:

o---o---o---o---o---o---o---o---o master
\
o---o---o---o---o subsystem
\
*---*---* topic

If subsystem is rebased against master, the following happens:

o---o---o---o---o---o---o---o master
\ \
o---o---o---o---o o'--o'--o'--o'--o' subsystem
\
*---*---* topic

If you now continue development as usual, and eventually merge topic to subsystem, the
commits from subsystem will remain duplicated forever:

o---o---o---o---o---o---o---o master
\ \
o---o---o---o---o o'--o'--o'--o'--o'--M subsystem
\ /
*---*---*-..........-*--* topic

Such duplicates are generally frowned upon because they clutter up history, making it
harder to follow. To clean things up, you need to transplant the commits on topic to the
new subsystem tip, i.e., rebase topic. This becomes a ripple effect: anyone downstream
from topic is forced to rebase too, and so on!

There are two kinds of fixes, discussed in the following subsections:

Easy case: The changes are literally the same.
This happens if the subsystem rebase was a simple rebase and had no conflicts.

Hard case: The changes are not the same.
This happens if the subsystem rebase had conflicts, or used --interactive to omit,
edit, squash, or fixup commits; or if the upstream used one of commit --amend, reset,
or filter-branch.

The easy case
Only works if the changes (patch IDs based on the diff contents) on subsystem are
literally the same before and after the rebase subsystem did.

In that case, the fix is easy because git rebase knows to skip changes that are already
present in the new upstream. So if you say (assuming you're on topic)

$ git rebase subsystem

you will end up with the fixed history

o---o---o---o---o---o---o---o master
\
o'--o'--o'--o'--o' subsystem
\
*---*---* topic

The hard case
Things get more complicated if the subsystem changes do not exactly correspond to the ones
before the rebase.

Note
While an "easy case recovery" sometimes appears to be successful even in the hard
case, it may have unintended consequences. For example, a commit that was removed via
git rebase --interactive will be resurrected!

The idea is to manually tell git rebase "where the old subsystem ended and your topic
began", that is, what the old merge-base between them was. You will have to find a way to
name the last commit of the old subsystem, for example:

o With the subsystem reflog: after git fetch, the old tip of subsystem is at
subsystem@{1}. Subsequent fetches will increase the number. (See git-reflog(1).)

o Relative to the tip of topic: knowing that your topic has three commits, the old tip
of subsystem must be topic~3.

You can then transplant the old subsystem..topic to the new tip by saying (for the reflog
case, and assuming you are on topic already):

$ git rebase --onto subsystem subsystem@{1}

The ripple effect of a "hard case" recovery is especially bad: everyone downstream from
topic will now have to perform a "hard case" recovery too!

BUGS
The todo list presented by --preserve-merges --interactive does not represent the topology
of the revision graph. Editing commits and rewording their commit messages should work
fine, but attempts to reorder commits tend to produce counterintuitive results.

For example, an attempt to rearrange

1 --- 2 --- 3 --- 4 --- 5

1 --- 2 --- 4 --- 3 --- 5

by moving the "pick 4" line will result in the following history:

3
/
1 --- 2 --- 4 --- 5

GIT
Part of the git(1) suite

NOTES
1. revert-a-faulty-merge How-To
file:///usr/share/doc/git-1.8.3.1/howto/revert-a-faulty-merge.txt

Git 1.8.3.1 05/23/2023 GIT-REBASE(1)

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