Knowledge gap

• knowing what to ignore or delete
• Files: .gitignore, …
• git merge conflicts (avoid most conflicts)
• how to avoid conflicts or resolve them.
• Revert back to older version (for everything & for only a single file)
• git remove (removed too much)

Knowing what to ignore or delete

http://gitignore.io

Merge conflicts

How to avoid

• Don't work on the same code
• Make small commits
• Integrate as fast as possible

Tools

• KDiff3
• SourceTree
• IntelliJ, or any proper IDE actually
• EditorConfig

Whitespace and CR/LF conflicts

Be aware that inconsistent formatting settings on your team's workstations can cause merge conflicts that are difficult to solve. Avoid these by using EditorConfig to share formatting settings.

Difficult because it can be hard to distinguish the important changes in between the new line changes or whitespaces.

Luckily most tools provide support to ignore whitespace.

Reverting back

Sometimes you just want to undo your changes, because 💩 happens.

Depending on which stage your changes are in, there's git revert and git reset to help you out.

Your changes are in your staging dir?

Use git reset to undo them.

Your changes are in a commit?

But you haven't pushed them to a remote yet?

You can simply modify your files the way you want, and git commit --amend.

And you have pushed them to a remote already

Then you can git revert, and create a new commit with the undo.

Exercise

Step 1: fork this repository

Step 2: do as instructed and keep on running git status in between steps.

Changing non pushed commit

git checkout exercise-start

Change the first sentence to Woke up in a squad car, jailed away for vagrancy.

Then run git commit -am "misheard lyrics" to both add and commit the changed file with a message.

We forgot to also change jailed away to busted down.

Let's do that now and change the first sentence to Woke up in a squad car, busted down for vagrancy.

Now we want to modify the previous commit that we haven't pushed yet to incorporate this new change, so do

git add lyrics.md
git commit --amend

And keep the previous commit message as "misheard lyrics".

Fixing a merge conflict

git merge origin/exercise-merge-conflict

We want only the second sentence without comma's.

Your end result should look like this:

Woke up in a squad car, busted down for vagrancy
Outside my cell it sure as hell looked like rain

Now that our merge conflict has been resolved, let's add our changed file to our staging directory with git add lyrics.md.

Reset a failed merge

Let's assume that we botched the merge completely and we want to try the merge again.

git reset --hard

If we wanted to retain our changes we could've just done git reset. --hard tells git we don't want any of our changes anymore and want to start clean again.

Perform the merge again with git merge origin/exercise-merge-conflict.

This time do the same modification but leave out the , in the first sentence as well.

Your end result should now look like this:

Woke up in a squad car busted down for vagrancy
Outside my cell it sure as hell looked like rain

Commit with git commit -am "merged without comma's".

Reverting a commit

If we do git log now, it should look a bit like this:

commit 00fae8debff7de2f02e06151edfa0ba27973d709
Merge: 31684e8 d1d8969
Author: Tim Schraepen <sch3lp@gmail.com>
Date:   Wed Mar 8 13:27:36 2017 +0100

    merged without comma's

commit 31684e8abda479d4ae1847ec592b7d893025f4d1
Author: Tim Schraepen <sch3lp@gmail.com>
Date:   Wed Mar 8 11:40:28 2017 +0100

    misheard lyrics

commit d1d8969fd87f4a1b6c1cde301afcd863916a03e8
Author: Tim Schraepen <sch3lp@gmail.com>
Date:   Wed Mar 8 11:39:09 2017 +0100

    who needs comma's anyway

commit 6dacd22fec2168a1752a9f265c25ad0d74198cde
Author: Tim Schraepen <sch3lp@gmail.com>
Date:   Wed Mar 8 11:35:23 2017 +0100

    init

Let's create a new file in the root directory to contain artists or whatever: touch artists.md.

Then add this file and commit it. Your git log should have a new top entry:

commit 93fe283cd8f5f1f6e1ac9be633d4c3b1552aa665
Author: Tim Schraepen <sch3lp@gmail.com>
Date:   Wed Mar 8 13:33:25 2017 +0100

    added artists

Our boss reads our commit history and was yelling that our repository isn't meant to host artist information, we only do lyrics and we do it good, god damn it!.

We could delete our artists.md and commit that, but it would make more sense to add more semantics to this event and git revert the commit that added the artists.md file.

git revert 93fe28

Note: Your commitish (the number-letter combination that identifies a commit) will look differently so don't just copy paste!

This will add a new commit that reverts the commit that introduced the artists file.

Your log should now look like this:

commit c9e124348db9cc4229cd471fd24874f686cc3a79
Author: Tim Schraepen <sch3lp@gmail.com>
Date:   Wed Mar 8 13:36:45 2017 +0100

    Revert "added artists"
    We only do lyrics and we do it good, god damn it.

    This reverts commit 93fe283cd8f5f1f6e1ac9be633d4c3b1552aa665.

Since we're rebels (FIGHT THE POWER!), let's add the artists.md file anyway and do a git commit --amend.

Note that you'll have to also add an artist or change the artists.md file in some way, otherwise git will notice the null operation of deleting an empty file and adding an empty file and tell you about it:

You asked to amend the most recent commit, but doing so would make
it empty. You can repeat your command with --allow-empty, or you can
remove the commit entirely with "git reset HEAD^".

Reverting a specific file to a previous version according to a commit

Let's add ##Micky Newbury as the first line of both the artists.md and lyrics.md files and commit them.

Change the top line in artists.md to ## Micky Newbury - 33rd of August and commit it as well.

Whoops! We were supposed to add that in the lyrics.md file, not in the artists.md.

Let's checkout the previous version of artists.md:

First get the commitish of the latest version

git log artists.md

commit b2f610b7ac232515106d8e7b7061db8b7babbada
Author: Tim Schraepen <sch3lp@gmail.com>
Date:   Wed Mar 8 14:43:49 2017 +0100

    added artist

commit 1e41e4a8e282aae345bb297636d8fb1fc6d2090e
Author: Tim Schraepen <sch3lp@gmail.com>
Date:   Wed Mar 8 13:52:22 2017 +0100

    added artist info

My latest version is b2f610, I want to checkout the one before that:

git checkout b2f610~ artists.md

The ~ represents the one before.

Now we can change the top line in lyrics.md to ## Micky Newbury - 33rd of August and commit both files again.

Note on renaming files to lowercase or uppercase

Here's a typical scenario:

You're just learning a new language and you're using another language's naming conventions.

e.g. You're working on a Java project, but you used .Net naming conventions for packages.

.Net convention says: Snakecase your package names: Vagrancy.

Java convention says: lowercase your package names: vagrancy.

Exercise

The exercise-snake branch contains a new directory com/lyrics/Vagrancy (mind the case). So let's check that out as our starting position.

git checkout exercise-snake

Now rename the directory com/lyrics/Vagrancy to lowercase com/lyrics/vagrancy and perform a git status.

nothing to commit? But, but, but, but I renamed the directory to lowercase!? What gives GIT?!

So how do we do this properly?

Let's reset back to our starting branch. Why can't we use git reset --hard?

We'll need to check out another branch first and then checking out the original exercise-snake branch (with the dir starting with a capital V).

git checkout master
git checkout exercise-snake

So if mv com/lyrics/Vagrancy com/lyrics/vagrancy doesn't work, maybe if I prepend it with git it might work?

Try it! I'm getting fatal: renaming 'com/lyrics/Vagrancy' failed: Invalid argument.

So let's just try it with an intermediary step:

git mv com/lyrics/Vagrancy com/lyrics/vagrancytmp
git mv com/lyrics/vagrancytmp com/lyrics/vagrancy
git status

Git recognized that we really wanted to rename it! Pure barry!

Finally commit this rename to lowercase.

Another way to do it without git mv is to rename it to a temp folder, commit that, then rename it to the actual lowercase folder and git commit --amend.

When you git show, git also tells you it recognized the rename:

rename from com/lyrics/Vagrancy/.gitkeep
rename to com/lyrics/vagrancy/.gitkeep

That's it!