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Merge pull request swcarpentry#388 from tgamblin/solutions-09-conflicts
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Add solutions for exercises 2 and 3 in 09-conflicts
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@iglpdc
iglpdc authored Mar 9, 2017
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181 changes: 178 additions & 3 deletions _episodes/09-conflict.md
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Expand Up @@ -294,9 +294,9 @@ We removed the conflict on this line

We don't need to merge again because Git knows someone has already done that.

Git's ability to resolve conflicts is very useful, but conflict resolution
costs time and effort, and can introduce errors if conflicts are not resolved
correctly. If you find yourself resolving a lot of conflicts in a project,
Git's ability to resolve conflicts is very useful, but conflict resolution
costs time and effort, and can introduce errors if conflicts are not resolved
correctly. If you find yourself resolving a lot of conflicts in a project,
consider one of these approaches to reducing them:

- Try breaking large files apart into smaller files so that it is less
Expand All @@ -320,6 +320,168 @@ consider one of these approaches to reducing them:
> What does Git do
> when there is a conflict in an image or some other non-textual file
> that is stored in version control?
>
> > ## Solution
> >
> > Let's try it. Suppose Dracula takes a picture of Martian surface and
> > calls it `mars.jpg`.
> >
> > If you do not have an image file of Mars available, you can create
> > a dummy binary file like this:
> >
> > ~~~
> > $ head --bytes 1024 /dev/urandom > mars.jpg
> > $ ls -lh mars.jpg
> > ~~~
> > {: .bash}
> >
> > ~~~
> > -rw-r--r-- 1 vlad 57095 1.0K Mar 8 20:24 mars.jpg
> > ~~~
> > {: .output}
> >
> > `ls` shows us that this created a 1-kilobyte file. It is full of
> > random bytes read from the special file, `/dev/urandom`.
> >
> > Now, suppose Dracula adds `mars.jpg` to his repository:
> >
> > ~~~
> > $ git add mars.jpg
> > $ git commit -m "Picture of Martian surface"
> > ~~~
> > {: .bash}
> >
> > ~~~
> > [master 8e4115c] Picture of Martian surface
> > 1 file changed, 0 insertions(+), 0 deletions(-)
> > create mode 100644 mars.jpg
> > ~~~
> > {: .output}
> >
> > Suppose that Wolfman has added a similar picture in the meantime.
> > His is a picture of the Martian sky, but it is *also* called `mars.jpg`.
> > When Dracula tries to push, he gets a familiar message:
> >
> > ~~~
> > $ git push origin master
> > ~~~
> > {: .bash}
> >
> > ~~~
> > To https://github.com/vlad/planets.git
> > ! [rejected] master -> master (fetch first)
> > error: failed to push some refs to 'https://github.com/vlad/planets.git'
> > hint: Updates were rejected because the remote contains work that you do
> > hint: not have locally. This is usually caused by another repository pushing
> > hint: to the same ref. You may want to first integrate the remote changes
> > hint: (e.g., 'git pull ...') before pushing again.
> > hint: See the 'Note about fast-forwards' in 'git push --help' for details.
> > ~~~
> > {: .output}
> >
> > We've learned that we must pull first and resolve any conflicts:
> >
> > ~~~
> > $ git pull origin master
> > ~~~
> > {: .bash}
> >
> > When there is a conflict on an image or other binary file, git prints
> > a message like this:
> >
> > ~~~
> > $ git pull origin master
> > remote: Counting objects: 3, done.
> > remote: Compressing objects: 100% (3/3), done.
> > remote: Total 3 (delta 0), reused 0 (delta 0)
> > Unpacking objects: 100% (3/3), done.
> > From https://github.com/vlad/planets.git
> > * branch master -> FETCH_HEAD
> > 6a67967..439dc8c master -> origin/master
> > warning: Cannot merge binary files: mars.jpg (HEAD vs. 439dc8c08869c342438f6dc4a2b615b05b93c76e)
> > Auto-merging mars.jpg
> > CONFLICT (add/add): Merge conflict in mars.jpg
> > Automatic merge failed; fix conflicts and then commit the result.
> > ~~~
> > {: .output}
> >
> > The conflict message here is mostly the same as it was for `mars.txt`, but
> > there is one key additional line:
> >
> > ~~~
> > warning: Cannot merge binary files: mars.jpg (HEAD vs. 439dc8c08869c342438f6dc4a2b615b05b93c76e)
> > ~~~
> >
> > Git cannot automatically insert conflict markers into an image as it does
> > for text files. So, instead of editing the image file, we must check out
> > the version we want to keep. Then we can add and commit this version.
> >
> > On the key line above, Git has conveniently given us commit identifiers
> > for the two versions of `mars.jpg`. Our version is `HEAD`, and Wolfman's
> > version is `439dc8c0...`. If we want to use our version, we can use
> > `git checkout`:
> >
> > ~~~
> > $ git checkout HEAD mars.jpg
> > $ git add mars.jpg
> > $ git commit -m "Use image of surface instead of sky"
> > ~~~
> > {: .bash}
> >
> > ~~~
> > [master 21032c3] Use image of surface instead of sky
> > ~~~
> > {: .output}
> >
> > If instead we want to use Wolfman's version, we can use `git checkout` with
> > Wolfman's commit identifier, `439dc8c0`:
> >
> > ~~~
> > $ git checkout 439dc8c0 mars.jpg
> > $ git add mars.jpg
> > $ git commit -m "Use image of sky instead of surface"
> > ~~~
> > {: .bash}
> >
> > ~~~
> > [master da21b34] Use image of sky instead of surface
> > ~~~
> > {: .output}
> >
> > We can also keep *both* images. The catch is that we cannot keep them
> > under the same name. But, we can check out each version in succession
> > and *rename* it, then add the renamed versions. First, check out each
> > image and rename it:
> >
> > ~~~
> > $ git checkout HEAD mars.jpg
> > $ git mv mars.jpg mars-surface.jpg
> > $ git checkout 439dc8c0 mars.jpg
> > $ mv mars.jpg mars-sky.jpg
> > ~~~
> > {: .bash}
> >
> > Then, remove the old `mars.jpg` and add the two new files:
> >
> > ~~~
> > $ git rm mars.jpg
> > $ git add mars-surface.jpg
> > $ git add mars-sky.jpg
> > $ git commit -m "Use two images: surface and sky"
> > ~~~
> > {: .bash}
> >
> > ~~~
> > [master 94ae08c] Use two images: surface and sky
> > 2 files changed, 0 insertions(+), 0 deletions(-)
> > create mode 100644 mars-sky.jpg
> > rename mars.jpg => mars-surface.jpg (100%)
> > ~~~
> > {: .output}
> >
> > Now both images of Mars are checked into the repository, and `mars.jpg`
> > no longer exists.
> {: .solution}
{: .challenge}
> ## A Typical Work Session
Expand Down Expand Up @@ -349,4 +511,17 @@ consider one of these approaches to reducing them:
> |4 | | |
> |5 | | |
> |6 | Celebrate! | `AFK` |
>
> > ## Solution
> >
> > |order|action . . . . . . |command . . . . . . . . . . . . . . . . . . . |
> > |-----|-------------------|----------------------------------------------|
> > |1 | Update local | `git pull origin master` |
> > |2 | Make changes | `echo 100 >> numbers.txt` |
> > |3 | Stage changes | `git add numbers.txt` |
> > |4 | Commit changes | `git commit -m "Added 100 to numbers.txt"` |
> > |5 | Update remote | `git push origin master` |
> > |6 | Celebrate! | `AFK` |
> >
> {: .solution}
{: .challenge}

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