Git Tutorial 7: What is HEAD?

Key Takeaways

Dear friends, in this tutorial we are going to learn what is head in git. Head is a reference to the most recent commit in the current branch in most of the cases. The reason I said most of the cases is because there are some cases where uh this is not the case and we will cover them later on. I have this git repository where I have bunch of commits which I can list using git log. Okay. Okay. So I have these three comets. Now head is nothing but a reference to this comet. Uh I can verify by running this command called get show head. This will show me the head commit. This is same as doing get show this particular commit. Okay. So they produce the same output. So I can say head is just a short form of writing this commit. Okay. Now let me make one more commit and see what happens to get. So I'm going to add one more line here and I will commit that change. So I added this and I will now commit this. Okay. So get commit minus m burger. Okay. When I do that uh and if I run get log I say this commit and when I do get show head it will now show me burger commit. So as you can see in the diagram the head pointer keeps on moving and it always not always but in majority of the cases it refers to the most recent comet. Okay. Now let me show you another another case where head had head could be useful and that is to do the diff. Now we have been running this get diff tool command in our previous tutorial. So this uh command is useful to show the difference between two commits. Okay. So I'm going to run gift get diff to run two commits. So for example uh from this commit to this commit this pizza line was added. Okay. And I want to see the difference between the snapshot of this and this. So the way you do it is by running get diff tool the older commit which is this. So I'm just going to copy paste that commit and the newer commit which is this. So again I'll be copying and pasting. When I do that uh the mold diff tool will open and it will show me the difference from left and right. You see this pizza line was added between those two commits. So this is my old code. This is my new code. Okay. Now the same thing you can do by using a head. So I can say head. Now remember head is here. So this comet will be head tilda one and this commit will be head tilda 2. So you always put uh the older commit first. So I will do head tilda 2 and held uh tilda one. You can just say like head minus two you know this is one and this is this is head this is head minus one head minus two so head minus 2 and head minus one okay and when you do that you will get the same output you'll see that in this particular commit pizza line was added okay so this command is just a short form of running this but the benefit here is that you don't have to remember the commit or copy paste this wrong commit ID you can just use this short form. So head h a refers to this head my head tilda one refers to this head tilda 2 refers to this particular commit id. Okay now u let's see how g internally manages this head pointer. Uh if you have your code repository open and if you have if you're showing uh the hidden repos hidden directories then there is always a directory in your current code directory. If this is not visible you can go to windows explorer option and choose the option to show hidden files. Okay but once you have directory open you will see bunch of files here and head is one of the files. Now when I open this head file I will see this. So it is referring to a master branch. Now if I have two branches uh for example I have when I do get branch I have second branch called thirsty. Now when I check out the second branch my head pointer will actually move to thirsty. So see now it updated this file and now I have thirsty uh in my head. Okay. Now let me discuss the scenario where head doesn't point to the most recent commit. That scenario is called detached head. So sometimes uh when you do get log you want to go to this previous commit. Okay. And based on that previous commit you want to make some changes. So you want to make this particular commit your base and then want to add further changes because you want to ignore this. In that case you will do get check out this commit. Okay. And let's see what happens when we run this command. Okay. It is showing me this message that you are in detached head state. Meaning head is not pointing to the most recent commit. it is at some older commit. Okay. And you can see that reflected here as well. Usually it's a branch name but now it is this particular thing. Okay. So um now your head is in a detached state and when I open my head file head is having this commit ID 4 BC etc. And that was this commit ID 4 BC etc. So you can see how git manages all of these things by using a simple text file. Okay. All right. So now I want to come out of the detached head state. In that case you can do get checkout master. And now you are at master. The pizza is the most recent commit. And when you do that you will come out of the detached head state. All right. Okay. So, that was all about head. Thank you for watching this video.