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Using branches

If you need help at any time, put your red sticky note on the back of your laptop. When you've finished the steps on both sides of this page, put your green sticky note on the back of your laptop.

Retrieving a particular commit

One of the key strengths of git is the ability to "go back" to a previous "snapshot" of a repository, either temporarily (to just see what's in it) or permanently (to revert back to that version).

Notice that every time you run git commit, there is a "commit hash" associated with the commit. For example, try running

git log

from inside your git repository. In each log entry, the first line shows the commit hash, e.g. :

commit fc3792a21ab443e52b55a61407b33aded5481877
Merge: 625b584 63a79bb
Author: Fraida Fund <[email protected]>
Date:   Sun Nov 6 13:55:21 2016 -0500

    Fixed merge conflicts

To play with a "snapshot" of my repository corresponding to a particular commit, I can check out that commit into a new branch, like this:

git checkout -b fixedmerge fc3792a21ab443e52b55a61407b33aded5481877

(Your comit hash will be different; use one from your log history.) Now if I run

git branch

I can see that my local repository has two branches, fixedmerge and master, and that I am currently on fixedmerge:

* fixedmerge
  master

Furthermore, if I examine the contents of my files, I can see that they are exactly as they were as of that commit.

I can switch back and forth between branches to see the different versions of my file:

git checkout master
git checkout fixedmerge

If I want to restore my master branch back to a previous commit, I can checkout the master branch and use

git checkout master
git revert --no-commit fc3792a21ab..HEAD
git commit
git push origin master

again, substituting your own commit hash. You don't have to use the full commit hash; you can just use the first part of it.

Work in new branch, merge back to master

Sometimes, you may want to work on a new feature or test something in its own branch, rather than on master. You can start a new branch (named new) with

git checkout -b new

Change your README.md, then run

git add README.md
git commit -m "Test branch feature"
git push origin new

where in your git push command, you supply the name of the branch you are working on instead of master.

If you want to integrate the changes from the new branch into the master branch, you can merge it:

git checkout master
git merge new
git push origin master

and then delete the new branch, once it's no longer needed:

git branch -d new