What exactly is a git commit?
Latest commits point to previous commits.
What exactly is a git branch?
What is the HEAD pointer?
- Git commit saves a commit object that points to the current state of your repo aka snapshot.
Commit and Tree
- The next commit will have a pointer to this commit.
- Git branch is a lightweight movable pointer to one of the commits.
- When we create a new branch it creates a pointer to the same commit we are currently working on.
- The current branch that is being worked on is pointed to by HEAD pointer,
git log --decoratecan be used to check this.
How to move the HEAD pointer?
Branch commits always create a new commit pointing back to the initial commit.
git checkout <branch>will move the HEAD pointer to that branch.- If we make a new commit to that branch the commit will point back to the commit which is pointed to by the master branch.
- Now, if we switch back to master and create commits, we will create a divergent history.
- This also makes merging branches easily because their parent is known.
Keep in mind with which branch the changes will get merged with.
Merge conflicts occurs only on editing same part of the code on the same file.
- Merge creates a new snapshot using the most recent ancestor of the two branches.
- Checkout the branch you want to merge with and write
git merge branch_name.
$ git checkout master Switched to branch 'master' $ git merge iss53 Merge made by the 'recursive' strategy.
- Merge conflicts occurs when same part of the same file has been modified on two different branches. Something like:
`<<<<<<< HEAD:index.html
======= >>>>>>> iss53:index.html`- Here master and iss53 branches have different content in index.html.
- We need to choose between either code above or below ========.
- After resolution we need to add the files again to mark the conflict as resolved
git branch --mergedgives a list of branch merged and using--no-mergedoption gives those that are not merged into the current branch that is checked out.
Consultation required to rename master branch, it may break everything.
git branch --move old_branch_name new_branch_namecan be used to rename branches.- To reflect this on the remote, use
git push --set-upstream origin new_branch_name. - To delete old branch use
git push origin --delete old_branch_name.
Remote branches are always named as remote_name/branch.
- Branches that are short lived and used for a single particular feature are called topic branches.
- Remote branches are named as remote/branch like
origin/master. - To get changes from remote branches we use
git fetch.This updates our origin/branch contents.
Upstream tells which local branch is corresponding to the remote branch.
- Local branches that have a direct connection with remote branch.
- When we track local branch with remote branch,
git pullwill bring all the latest remote changes to your local branch. - Use
git checkout --track origin/serverfixto create a local serverfix branch that tracks the remote one. - To see the branches that are being tracked and their ahead/behind status:
git branch -vv iss53 7e424c3 [origin/iss53: ahead 2] Add forgotten brackets master 1ae2a45 [origin/master] Deploy index fix
Rebasing is no different than merge.
Rebasing helps give clean history.
Mostly used when contributing.
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Rebasing is another way of merging branches.
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In rebasing the branch to be merged is updated with patches made i.e. the diff statements.
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git checkout experiment & git rebase masterresults in following:
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git checkout master & git merge experimentresults in a fast-forward merge:
- End product of rebase is no different than merge.
- The only difference is in the merge log history, which appears as a series.
- Rebase is used when contributing to a repo, so that the merger only needs to do fast forward merge and the merge is cleaner.