In git, what is the difference between merge

2018-06-17 10:38:30

I'm new to git and I'm trying to understand the difference between a squash and a rebase. As I understand it you perform a squash when doing a rebase.

Both git merge --squash and git rebase --interactive can produce a "squashed" commit.
But they serve different purposes.

git merge --squash abranch

will produce a squashed commit on the destination branch, without marking any merge relationship.
(Note: it does not produce a commit right away: you need an additional git commit -m "squash branch" )
This is useful if you want to throw away the source branch completely, going from (schema taken from SO question):

 git checkout stable

      X                   stable
     /                   
a---b---c---d---e---f---g tmp

to:

git merge --squash tmp
git commit -m "squash tmp"

      X-------------------G stable
     /                   
a---b---c---d---e---f---g tmp

and then deleting tmp branch.

git rebase --interactive

replays some or all of your commits on a new base, allowing you to squash (or more recently "fix up", see this SO question), going directly to:

git checkout tmp
git rebase -i stable

      stable
      X-------------------G tmp
     /                     
a---b

If you choose to squash all commits of tmp (but, contrary to merge --squash , you can choose to replay some, and squashing others).

So the differences are:

merge does not touch your source branch ( tmp here) and creates a single commit where you want.

rebase allows you to go on on the same source branch (still tmp ) with:

a new base

a cleaner history

Merge squash merges a tree (a sequence of commits) into a single commit. That is, it squashes all changes made in n commits into a single commit.

Rebasing is re-basing, that is, choosing a new base (parent commit) for a tree. Maybe the mercurial term for this is more clear: they call it transplant because it's just that: picking a new ground (parent commit, root) for a tree.

When doing an interactive rebase, you're given the option to either squash, pick, edit or skip the commits you are going to rebase.

Hope that was clear!

Merge commits: retains all of the commits in your branch and interleaves them with commits on the base branch 在这里输入图像描述

Merge Squash: retains the changes but omits the individual commits from history 在这里输入图像描述

Rebase: This moves the entire feature branch to begin on the tip of the master branch, effectively incorporating all of the new commits in master

在这里输入图像描述