Git Tutorial: Fixing Common Mistakes and Undoing Bad Commits

hey how's it going everybody in this video we're going to be looking at a few common scenarios and get where you can find yourself needing to undo some mistakes or even roll back some bad commits now some of these commands will change the get history and some will not and we're gonna take a look at exactly what that means here in a second now this will be a slightly more advanced get walkthrough and we're going to assume that you already know the basic command line functionality of git if you aren't familiar with basic git commands or how git works I do have a video on getting started with git in the command line if you would like to watch that video first but with that said let's go ahead and get started so let's take a look at the sample repository that I have set up here so if I do an LS - la within this directory you can see that I have this calc py file and I also have that count py file pulled up in my text editor over here and you can also see that we have the dot git directory here which just means that we are within a git repository so now if I run a git status you can see that currently our working directory is clean if I do a git log then you can see that we've only had one commit so far it's just the initial commit and also if I run a git branch you can see that we have another branch here called subtract feature so both the subtract feature branch and the master branch are currently exactly the same they both only have that one initial commit but for now we're not going to bother with the subtract feature branch we'll take a look at that here in a little bit so let's look at our first example of a mistake that you might want to undo so first we're going to say that we've made changes to a file and after a while we realized that we don't want any of the changes that we've made so whatever whatever we've done it just isn't right and we want to go back to the way things were so for this example I'm just going to type in a bunch of gibberish here into the text editor but more realistically in the real world this would likely be a bun code that for one reason or another just isn't right and you want to go back to the way that things were so for this example if I go over here and do they get status you can see that we have modified the file if I do they get diff you can see all the gibberish lines that we've put in there now the way that we can fix this is to just use a simple git checkout so what I'm going to do here is a get checkout calc py and if I hit enter there now if I do it get status you can see that our working directory is clean and if I do a get diff you can see that we don't have any changes and if I go over here to the file and this reloads over here you can see that we are back to the way that things were after we made our initial commit so now let's actually make some changes to our file that we do want to commit to our repository so I'm going to come in here and change the subtract function and I'm just going to do a return X minus y so that's what we want so now I'm going to go back over here to our terminal now if I run a get status you can see that the file has been modified in the working directory and I'm going to add that to the staging area and now if I do another get status you can see that that file is ready to be committed so now I'm going to go ahead and commit this file but let's say that we make a git commit and accidentally mess up our commit message so I'm going to say that we completed the multiply function which is wrong because we completed the subtract function so I'm going to go ahead and commit that with the bad commit message so now if I do a git log you can see that we've made the commit but the message is wrong so how do we modify this message without doing another commit well to do that we can just do another commit with the - - amend option so if I do a git commit dash - amend that I can type in - M for my message and I'm just going to say completed subtract function so now if I do a get log here you can see that we haven't added any more commits we still just have the two commits but we have changed this commit message on our last commit which is what we wanted now I do need to point out that this unique hash here is different than it was before we change the commit message now that's because the commit message is part of the commit and changing it will also change the hash and when the hash changes that means that it changed the get history so we only want to ever change the get history when we are the only ones who have had access to the changes that we've made so if we've pushed our changes for other people to see and pull from then we do not want to change to get history because it can cause problems with their repositories so later in this video we're going to look at some ways in which we can make corrections without changing to get history but as long as we're the only ones who have seen our changes then changing the history isn't necessarily a bad thing and it also makes for cleaner commits so in the case of a bad commit message this is likely something that you'll notice right away and can fix it right on the spot like we just did now kind of a similar scenario is that instead of accidentally committing the wrong message let's say that we accidentally left off a file that we meant to commit so in this example let's say that I meant to create a git ignore file and I wanted to add it to that last commit so I'm going to create a dot get ignore file here and now let me go ahead and run a git status and also let me add that to the staging area so I'll do the get add get ignore so now it's in our staging area but we don't want to make a new commit let's so for this example we're saying that we wanted that to be a part of the last commit so again we're just gonna do the git commit bass - amend like we did before but this time it's going to do it with a file so if I hit enter here now it's going to bring up this interactive editor where we can change the get commit message if we want now notice here that this is the same get commit message from our previous commit now we don't want to change the message in this case so I'm just going to save and close out so now I'm going to do a git log and you can see that we still just have the two commits that we had before now if I do a git log - - stat this will show us the files that were changed within the commit and you can see here that the git ignore file is now part of the last commit where we did the completed the subtract subtract function now once again just to point out this unique hash is now different so we once again change to get history so just one more time just to remind you only do this type of thing if you haven't pushed your changes yet to other people so now if I do a git log and then I do a git branch so now we see our subtract feature branch and now just say that it hits us all of a sudden that we've been making all of these commits to the master branch by accident really we've been meaning to make these commits to our subtract feature branch now this is a fairly common mistake to commit to the wrong branch because when you switch back and forth sometimes you just forget exactly where you are and end up committing to the wrong branch by accident so how do we move this commit right here this one b8 1:8 how do we move that commit to our feature branch now to be clear here exactly what we want to do is our goal is to move this commit to our subtract feature branch and then we want to return our master branch back to the state of only having the single initial commit so the way that we're going to do this is we're going to use git cherry-pick and cherry-pick creates a new commit based off of our original so in this case our original is going to be this top commit here now cherry-pick only creates a new commit based off of that committed doesn't delete the original after a cherry picks it so let me clear my screen here and so the process that you go through to do and get cherry pick this first you want to do a get log because we want to grab the the hash of the commit that we want to cherry pick so we don't have to grab the entire hash usually six or seven characters is fine so I'm just going to copy this here and now I want to do a git checkout on my subtract feature branch so now I'm going to switch to my subtract feature branch and now from that branch if I do a git log you can see that we only have the initial commit now I'm going to do a git cherry-pick and I'm going to paste in the hash that I had copied from the master branch so now if I hit enter there and now I do a git log now you can see that we brought that commit for the complete subtract function if we brought that commit over to our subtract feature branch so now we have that commit on our feature branch but it still exists on our master branch because cherry-pick doesn't delete commits but we don't want that commit on our master branch we never meant to commit it there to begin with so how do we get rid of it so to do this we're going to use a git reset so I'm going to do a git checkout one master and now I'm going to do a git log so that we can see the commits that we have now there are three different types of resets that we should know about these are get reset soft get reset mixed which is the default and get reset hard so first let's run through all of these so first let's run get reset soft to try to return to our initial commit so I'm going to grab the hash from this initial commit and copy that and now I'm going to do a git reset - - soft and then I'm going to paste in that hash of our initial commit so now if I do a git log you can see that we no longer have that second commit which is good that's what we wanted but let's also look at our get status now you can see that we have some files and our staging area so soft will reset us back to the commit that we specified but it will keep our changes that we've made in the staging directory so we didn't lose any of our work so in this case our work refers to the addition of the dot get ignore file and the modifications that we made to the calc not py file so that is a soft reset let's look at a mixed reset which is the default so again I'm going to grab the hash of the initial commit and this time let's do a git reset and I'm just going to paste in the hash because without any additional options it will default to mixed so let's go ahead and run that and now let's look at our get log we only have the one commit which is good but now if I do a get status you can see just like get reset soft it kept the changes however now these changes aren't in the staging area and now they're in the working directory so it's very similar to get reset soft but the files are either put in the staging or working directory based on which one you specify but in this example reboot we really don't want our changes we really just want to go back to that initial commit and have everything the way that they were so again let's copy the initial commit hash and this time we're going to try a get reset hard so get reset hard is going to make all of our tracked files match the state that they were in at the hash that we specify and you have to be careful with get reset hard because it will get rid of your changes but in this example that's what we want that's what we want so I'm going to do a git reset that's that's hard and paste in that hash and now if I do a get logged you can see that we have the one commit and now I'm going to run get status so notice that the modifications that we made to the calc py file are gone but that the dot did ignore file is still there now if you remember I said that the get reset hard reverts all of the tracked files back to the state that they were but it leaves any untracked files alone so we can see here that we still have some leftovers with the get reset hard but luckily getting rid of untracked files is extremely simple so to get rid of untracked files we can just use get clean so if I do a get clean and then I'm going to specify the D and the F option so the option gets rid of any untracked directories and the F gets rid of any untracked files so if I run that now if I do a git status you can see that our working directory is clean and that dot get ignore file is gone now that clean command is a good command to know because it actually comes in handy more often than you think for example one time I was accidentally accidentally unzip the file within my git repository and it created just a ton of untracked files and subdirectories and I could have gone through and tried to pick all those out manually and delete all of them but the easiest way to remove all those untracked files is just with this single get clean command ok so we learned that the get reset hard totally totally deletes all of our changes but what if you accidentally ran that and it turns out that you did need some of those changes so let's pretend for the sake of this walkthrough that we don't have those changes still save to the subtract feature branch and we thought that the reset deleted all of the changes that we've made so if you did run and get reset hard on some changes that you really needed then are you completely out of luck well not entirely so you could be out of luck if a lot of time has gone by since you ran that get reset I don't know the exact amount of time but I think get garbage collects those commits after 30 days or so but get ref log is what we're going to want to use here so get ref log shows commits in the order of when you last reference them so let me run a git ref log here and you can see that it kind of shows us exactly walkthrough of exactly what we've been doing so you can see here at the bottom is where I made my initial commit and then we committed our complete multiply multiply function which was wrong and then you can even see where you amended commits so this was an amended commit where we changed our message and another amend that's where we added the dot getting more file and it shows us that we checked out and moved from master to subtract feature and then did our cherry-pick and our check out and then our reset now if you'd accidentally got rid of files that you didn't mean to get rid of then so for this example I'm going to grab the hash before the reset and copy that and I'm gonna do a git checkout of that hash and now from here I'm gonna run a git log so you can see when I run a get log from this hash that we have our changes back this is the commit that we reset and got rid of all those changes now right now we are in a detached head state now I'm not going to go fully into what this means but basically it means that we aren't on a branch and where we currently are it will be trashed at some point in the future so to save these changes we need to make a branch from it so from here I'm gonna do a git branch and I'm just going to call this backup and now if I run get the branch command to look at all my branches you can see that currently were any attached head state and that's we'll get garbage collected at some point and now we have our master branch our subtract feature branch we also have this backup branch so now let me check out the master branch and now from the master branch if I do a git branch you can see that we still have our backup branch so those changes that we thought that we'd lost now we have those in this branch here so just to confirm that we still have those changes let's do a git checkout of that backup branch and now from here let's do it get log and now you can see that we have those changes that we thought that we'd lost so the get ref log can really be a lifesaver if you thought that you had lost some critical files that you really didn't mean to delete or that if you accidentally did a reset on something the ref log can really help you out if you know how to use it okay so in these examples so far I mentioned that you shouldn't change to get history if other people have pulled those changes already well what if you are in a situation where you really need to undo some commits but other people have already pulled those changes so in a situation like that you're gonna want to use get revert revert creates new commits to reverse the effect of some earlier commits so this way you don't rewrite any history just to clarify that it's not going to modify or delete our existing commits that we've made it's going to create new commits on top of those that completely undo all of the changes so that our history remains intact so just to show an example of this I'm gonna run a git log and you can see that we have our two commits here so now what if this completed subtract function I wanted to undo that but other people have already checked that out well I can just copy the hash here and I'm going to do a git revert and then paste in that hash and now it's going to come up here with a message and I'm just gonna save that and exit out of that and now if I close out of there and do a git log you can see that we now have three commits and these two bottom commits are completely untouched both of their hashes are still the same as they were before the pervert now we have this additional commit that says that it reverted the complete subtract function so if I go over here to my account dot py file and reload it you can see that it's it undid that return statement that we typed in now one nice little trick with the get if command is that if I do a to get logged here and then I do a get death of this hash and this hash here it's going to show me the difference between the complete subtract function commit and then the reverted version of that so you can see that whenever I compare these two commits all it did was go in here and it completely it's all all the changes that we made in our complete subtract function commit and then it just redid or undid those so for that commit we took out the pass line and added in the return X minus y line and in the revert it took out the return x minus y and added in the past so it just did the complete opposite so now whenever you push these changes and somebody else pulls those down their history is not going to be corrupted because all of this history is the same and all they're going to get is these are these new commits that undid those previous commits well that about does it for this video I hope that these get tips on how to undo some of your mistakes and roll back some previous commits I hope that this was useful for you all if you do have any questions just ask in the comment section below be sure to subscribe for future get videos and thank you for watching

Channel: Corey Schafer

Views: 306,016

Rating: 4.9757199 out of 5

Keywords: Git (Software), Git Reset, Git Revert, Git Amend, Git Cherry-Pick, Git Cherry Pick, Git, Git Tutorial, Git Tutorials, Git for Beginners, Git command-line, Command-Line, Terminal, Software, Git Basics, Git How-to, Git How to, Software Engineering (Industry), Computer Science (Field Of Study), Programming, Programming Tutorials, Version Control, How-to (Website Category), Commit, Git commit

Id: FdZecVxzJbk

Length: 21min 31sec (1291 seconds)

Published: Mon Oct 26 2015