Join Kevin Skoglund for an in-depth discussion in this video Merging conflicts, part of Git Essential Training.
We now know how to merge one branch into another and Git does a really good job at figuring out how to merge those together. For example, let's say that we've our index.html file and in the master branch we make a change to the top of the index.html file, somewhere near the top of html we make an edit. Then we have another branch that we're merging in, and we made a change near the bottom of the index.html file. That's not a problem for Git. Git sees those, it recognizes the line numbers and realizes that those are not next to each other, and it takes both of those changes and incorporates them into one composite document.
Having two versions of a single document is not a problem, most of the time. However, a conflict occurs when there're two changes to the same line or set of lines in two different commits, because then Git can't decide which one to use or how to merge them together and so we get a merge conflict. And this is the one headache about working with branches is resolving merge conflicts. So let's first talk about what it is, and then we can talk about how to solve them. So just a quick example, let's say that we have our master branch, and we have a line somewhere in one of our HTML files this says Git is great, and it has <span> tags around it.
From my master branch we create a new branch, we'll call it the new_styles branch. And we start making edits over there. We got all sorts of commits going on, at the same time we're switching back to master, and we're making edits back there as well. One of the edits that we commit to master is that we change the <span> tags into <strong> tags, and then we keep making more commits, we switch back to new_styles, we're making more commits over there. At some point, we make an edit in the new_styles branch so that we change the <span> tags into <em> tags. So now we've two different versions of this line. In the master branch it has <strong> tags around it, in the new_styles branch it's got <em> or emphasis tags around it.
So when we go to merge new_styles back into master, Git doesn't know which one of these we prefer. Git says I can't choose between these. I don't have any idea what's your intention was, so I need you to tell me. So git will mark the conflict and wait for you to fix the problem. Let's try this in our explore_california project. The page I'm going to use to generate a conflict is going to be this mission.html page so just open that up real quick so you can see it. And what I want to do is I'm going to create a merge conflict in this text down here. So in order to that, we have to create the conditions that will make that happen.
The first thing is let's make a new branch, so git checkout -b text_edits. Now remember, checkout -b is checkout as a new branch, or create a branch, and then switch to it. Now in my new branch let's open up mission.html, and this is just a text_edit branch, the idea here is it's a branch dedicated to making edits to the text. So I'm going to scroll down to that block of text, and let's make some edits here. We are passionate about Californian preserving the abundant resources that make it so unique. Our goal at Export California is transform your vacation into adventure that will educate, inspire, and energize you unlike any other.
Let's take away unlike any other, it'll just energize you. Okay, that's good so that's an edit to line 65 right here. All right, now let's see line 66. Our tours are crafted around our central mission, and are deigned to engage you in a unique and fulfilling way. All our tours are sensitive to the environment, and will provide you will the opportunity to explore California in your own way. Let's say, they're, cut this, and we will say they're environmentally sensitive, instead. Okay, so environmentally sensitive, so we made edit to line 66, and then let's comedown here to line 67, let's change this quote here into being have.
It's simply really, we'll leave that, and let's see, we ask ourselves one question, we'll say we ask ourselves a question. And I think that's good. Okay, so we have made an edit to line 67. So 65, 66, and 67 have all had edits. Let's make one to line 68, we have worked for a tour company. Okay, so now each one of those lines has some edits in it. So we could go on and you keep editing as much as you like. Let's now save that document and close, now we're on our text_edits branch, we know that we've made changes, we can see that with git status.
So now we can do a commit, and we'll do that with git commit, and I will use the -am option, and then my message will be "Text edits on mission page." Okay, so now I've made that commit to my text_edits branch. So now let's go back and let's check out our master branch. All right, so now we're back in the master branch, this does not have that edit in there, let's go in to mission.html, and let's scroll down to that big block of text. You'll see that those changes that I made, like we've, right, those are all gone.
We have the old version and the change that I'm going to make here is that I'm going to change the quotes here. See if we still have this up, these are straight double quotes. You can see those here. What I want to do is turn those into curly quotes. So let's go back here, and we'll make this one left double quote, and this one is right double quote. Okay, and let's while we are at it, let's go ahead and make this one &rsquo, and that will take care of that, let's copy that, let's paste that in here for the tours, we are basically just making all of these curly.
Okay, so all of those have now been turned into curly ones. I may have missed some, in fact, here is one right here, and right single quote. Okay, so let's close that document now, and let's make this commit, git commit and "Replaces double quotes with curly quotes," actually I can do it with single quotes too, not just the double quotes, let's say, Replace straight quotes. Okay, so now let's remind ourselves what we have, git log --oneline, this is in the master branch, oops, some typo there.
Replaces straight quotes with curly quotes is the merge that comes right after the merge with this shorten_title branch. If we check the same thing, put in our text_edits branch, you'll see that we have our shorten_title merge here, and then we have our new commit here. But those two commits change some of the same conflict. So let's try and merge now, so just to remind you, here are our branches. We're going to do git merge, and then we can say, text_edits. Says auto-merging CONFLICT, merge conflict in, and it gives us a list of all the things that have conflicts, mission.html.
Automatic merge failed, fix conflicts and then commit the result. Okay, so now notice that my branch now says master and MERGING, right? I'm not fully on my master branch, I'm in the middle of a merge, it's letting me know that. Let's take a look, if we do git status, look what it comes up and tells me, unmerged paths right here, it tells me to use add and remove on them, to mark the resolution, tells me both have been modified, both versions of mission.html, and so nothing is ready to commit yet. I need to fix these problems.
Let's open up mission.html, and let's scroll down to see how Git marked those problems, here it is. This is what is in the HEAD, which is remember, the master branch, the current branch that I'm on. And it tells me those lines, and then it's got a bunch of equal signs, and then it's got another block here, and it tells me that that's what's in the text_edits branch. So now it's up to me to go through and decide which one of these I want. But there are three lines that were different in each one, and each one had some conflicts in it.
Now that we see how merge conflicts occur, and we see that Git marks them using symbols like this, we're ready to talk about how to resolve these merge conflicts, and we'll do that in the next movie.
- Exploring the history of version control
- Installing Git on Mac, Windows, and Linux
- Initializing a repository
- Writing useful commit messages
- Understanding the Git three-tree architecture
- Tracking when files are added, edited, deleted, or moved
- Viewing change sets and comparing versions
- Undoing changes and rolling back to previous versions
- Ignoring changes to select files
- Creating and working with code branches
- Merging branches and resolving merge conflicts
- Stashing changes for later
- Working with hosted repositories and remote branches
- Developing an effective collaboration workflow
Skill Level Beginner
Q: In the Chapter 10 movie "Configuring the command prompt to show the branch," when I type the function "__git_ps1," I do not get the expected result.
A: The function "__git_ps1" was recently moved to a new file, .git-prompt.sh, as described here: https://github.com/git/git/commit/af31a456b4cd38f2630ed8e556e23954f806a3cc.
We will update the video. In the meantime, you may do the same steps you do for .git-completion.bash, but a second time using ".git-prompt.sh" as shown here: https://github.com/git/git/blob/master/contrib/completion/git-prompt.sh.
Q: When I use the code the instructor advises in the above video ("git config --global user.name "Nelda Street"), I still get an "Illegal Instruction" error. I have OS 10.6.8. Am I doing something wrong?
A: The current installer version of git isn't compatible with older Mac OS versions.
1. To add "-mmacosx-version-min=10.6" as described here:https://stackoverflow.com/questions/14268887/what-is-the-illegal-instruction-4-error-and-why-does-mmacosx-version-min-10https://stackoverflow.com/questions/10177038/illegal-instruction-4-shows-up-in-os-x-lion
2. Or to use the version of git that comes with Xcode, or to use homebrew to install git instead.http://superuser.com/questions/697144/installed-git-not-sure-how-to-get-it-working