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[MUSIC]

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You have two branches, both have changes
you need but when you check one out,

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the changes on the other
are no longer available.

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How do you get access to both at once?

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You merge the branches.

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Merging takes the contents of
your files from one branch and

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merges them with the contents
of your files on another branch.

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You can merge any branch into any other
branch, although it's most commonly used

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to bring the contents of a topic
branch into the master branch.

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We've discovered a problem with our code.

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If we run our main
program we get an error.

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It points to an error
in our decoder.rb file.

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Let's go fix that.

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The problem is that our program is trying
add a letter onto the end of the string

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whether that letter was actually found
in the hash full of keys or not.

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So we need to make it so
that the letter is only added

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on in the event that
the key is actually found.

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Again, don't worry if you don't
understand all the details of this.

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It's not essential to knowing
what's going on with the git repo.

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Lets go back to our terminal real quick
and try this to make sure it works.

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We're still not getting any output, but at
least we're not getting any more errors.

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Now, as always, code like this should go
on a topic branch not your master branch.

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We wanna be sure our topic branch
is based off the master branch, so

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let's check that out, git checkout master.

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So I'm gonna check out a new
topic branch to hold this code,

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we'll call it fix-nils,
git checkout -b fix-nils.

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And then we'll commit this
code to that new branch,

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we'll stage the decoder.rb
file with git add decoder.rb.

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And we'll make a commit, git commit
-m fix error with missing letters.

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If we run git log we'll be
able to see the new commit.

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These code changes will only
exist on the fix-nils branch.

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So for example, if we were to checkout the
master branch with git checkout master,

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and then if we refresh our editor
we can see that those changes

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don't exist here on the master branch.

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The commit doesn't exist on
the master branch's history either.

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Now that we have the master
branch checked out,

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let's merge our fix-nils branch into it.

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We do that with the git merge command,
git merge and

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then the name of the branch we want to
merge into the current one, fix-nils.

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So that'll take the commits
from our fix-nils branch and

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merge them into the master branch.

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Now if we run git log,
We'll see our fix error

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with missing letters commit
here on the master branch.

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And if we go refresh our editor again
we'll see that our code changes

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are visible on the master branch as well.

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Notice in the output for
the merge command it says Fast-forward.

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This is because we based the fix-nils
branch on the master branch, and

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we didn't make any additional commits to
the master branch before merging fix-nils

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into master.

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So git merge was able to bring
the changes from the fix-nils

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branch to the master
branch by simply moving

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the master branch pointer forward
to the latest commit on fix-nils.

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Normally, merges are a little
more complex than this, and

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it's not possible to git to fast forward.

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We'll see an example of
this in an upcoming video.

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You don't have direct control over whether
a merge is done by fast forwarding or

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not, so it's not something
you'll have to remember.

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You should just be aware that fast
forward merges can happen under certain

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circumstances, and

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that the resulting history looks
a little different than other merges.

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So now our bug fix is available
on the master branch.

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No errors.

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One last thing,

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now that we've merged the changes,
we don't need the fix-nils branch anymore.

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In fact, having it around could confuse
you later if you don't remember what

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it's for.

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So we need to delete it.

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We do that by running the git branch
command and passing it the -d option,

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followed by the name of the branch
we want to delete, fix-nils.

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If the branch weren't merged we'd
get a warning before deleting it.

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But because we've merged the branch into
another branch, git just goes ahead and

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deletes it for us.

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If we run git branch again we'll see
that the fix-nils branch is gone.

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So now we've created the topic branch and
merged it into our master branch.

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You can use the same process to
merge any two branches you want.

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In the next video, we'll merge changes for
master into a topic branch.