{"rowid": 31, "title": "Dealing with Emergencies in Git", "contents": "The stockings were hung by the chimney with care,\nIn hopes that version control soon would be there.\n\nThis summer I moved to the UK with my partner, and the onslaught of the Christmas holiday season began around the end of October (October!). It does mean that I\u2019ve had more than a fair amount of time to come up with horrible Git analogies for this article. Analogies, metaphors, and comparisons help the learner hook into existing mental models about how a system works. They only help, however, if the learner has enough familiarity with the topic at hand to make the connection between the old and new information.\n\nLet\u2019s start by painting an updated version of Clement Clarke Moore\u2019s Christmas living room. Empty stockings are hung up next to the fireplace, waiting for Saint Nicholas to come down the chimney and fill them with small treats. Holiday treats are scattered about. A bowl of mixed nuts, the holiday nutcracker, and a few clementines. A string of coloured lights winds its way up an evergreen.\n\nPerhaps a few of these images are familiar, or maybe they\u2019re just settings you\u2019ve seen in a movie. It doesn\u2019t really matter what the living room looks like though. The important thing is to ground yourself in your own experiences before tackling a new subject. Instead of trying to brute-force your way into new information, as an adult learner constantly ask yourself: \u2018What is this like? What does this remind me of? What do I already know that I can use to map out this new territory?\u2019 It\u2019s okay if the map isn\u2019t perfect. As you refine your understanding of a new topic, you\u2019ll outgrow the initial metaphors, analogies, and comparisons.\n\nWith apologies to Mr. Moore, let\u2019s give it a try.\n\nGetting Interrupted in Git\n\nWhen on the roof there arose such a clatter!\n\nYou\u2019re happily working on your software project when all of a sudden there are freaking reindeer on the roof! Whatever you\u2019ve been working on is going to need to wait while you investigate the commotion.\n\nIf you\u2019ve got even a little bit of experience working with Git, you know that you cannot simply change what you\u2019re working on in times of emergency. If you\u2019ve been doing work, you have a dirty working directory and you cannot change branches, or push your work to a remote repository while in this state.\n\nUp to this point, you\u2019ve probably dealt with emergencies by making a somewhat useless commit with a message something to the effect of \u2018switching branches for a sec\u2019. This isn\u2019t exactly helpful to future you, as commits should really contain whole ideas of completed work. If you get interrupted, especially if there are reindeer on the roof, the chances are very high that you weren\u2019t finished with what you were working on.\n\nYou don\u2019t need to make useless commits though. Instead, you can use the stash command. This command allows you to temporarily set aside all of your changes so that you can come back to them later. In this sense, stash is like setting your book down on the side table (or pushing the cat off your lap) so you can go investigate the noise on the roof. You aren\u2019t putting your book away though, you\u2019re just putting it down for a moment so you can come back and find it exactly the way it was when you put it down.\n\nLet\u2019s say you\u2019ve been working in the branch waiting-for-st-nicholas, and now you need to temporarily set aside your changes to see what the noise was on the roof:\n\n$ git stash\n\nAfter running this command, all uncommitted work will be temporarily removed from your working directory, and you will be returned to whatever state you were in the last time you committed your work.\n\nWith the book safely on the side table, and the cat safely off your lap, you are now free to investigate the noise on the roof. It turns out it\u2019s not reindeer after all, but just your boss who thought they\u2019d help out by writing some code on the project you\u2019ve been working on. Bless. Rolling your eyes, you agree to take a look and see what kind of mischief your boss has gotten themselves into this time.\n\nYou fetch an updated list of branches from the remote repository, locate the branch your boss had been working on, and checkout a local copy:\n\n$ git fetch\n$ git branch -r\n$ git checkout -b helpful-boss-branch origin/helpful-boss-branch\n\nYou are now in a local copy of the branch where you are free to look around, and figure out exactly what\u2019s going on.\n\nYou sigh audibly and say, \u2018Okay. Tell me what was happening when you first realised you\u2019d gotten into a mess\u2019 as you look through the log messages for the branch.\n\n$ git log --oneline\n$ git log\n\nBy using the log command you will be able to review the history of the branch and find out the moment right before your boss ended up stuck on your roof.\n\nYou may also want to compare the work your boss has done to the main branch for your project. For this article, we\u2019ll assume the main branch is named master.\n\n$ git diff master\n\nLooking through the commits, you may be able to see that things started out okay but then took a turn for the worse.\n\nChecking out a single commit\n\nUsing commands you\u2019re already familiar with, you can rewind through history and take a look at the state of the code at any moment in time by checking out a single commit, just like you would a branch.\n\nUsing the log command, locate the unique identifier (commit hash) of the commit you want to investigate. For example, let\u2019s say the unique identifier you want to checkout is 25f6d7f.\n\n$ git checkout 25f6d7f\n\nNote: checking out '25f6d7f'.\n\nYou are in 'detached HEAD' state. You can look around,\nmake experimental changes and commit them, and you can\ndiscard any commits you make in this state without\nimpacting any branches by performing another checkout.\n\nIf you want to create a new branch to retain commits you create, you may do so (now or later) by using @-b@ with the checkout command again. Example:\n\n$ git checkout -b new_branch_name\n\nHEAD is now at 25f6d7f... Removed first paragraph.\n\nThis is usually where people start to panic. Your boss screwed something up, and now your HEAD is detached. Under normal circumstances, these words would be a very good reason to panic.\n\nTake a deep breath. Nothing bad is going to happen. Being in a detached HEAD state just means you\u2019ve temporarily disconnected from a known chain of events. In other words, you\u2019re currently looking at the middle of a story (or branch) about what happened \u2013 and you\u2019re not at the endpoint for this particular story.\n\nGit allows you to view the history of your repository as a timeline (technically it\u2019s a directed acyclic graph). When you make commits which are not associated with a branch, they are essentially inaccessible once you return to a known branch. If you make commits while you\u2019re in a detached HEAD state, and then try to return to a known branch, Git will give you a warning and tell you how to save your work.\n\n$ git checkout master\n\nWarning: you are leaving 1 commit behind, not connected to\nany of your branches:\n\n  7a85788 Your witty holiday commit message.\n\nIf you want to keep them by creating a new branch, this may be a good time to do so with:\n\n$ git branch new_branch_name 7a85788\n\nSwitched to branch 'master'\nYour branch is up-to-date with 'origin/master'.\n\nSo, if you want to save the commits you\u2019ve made while in a detached HEAD state, you simply need to put them on a new branch.\n\n$ git branch saved-headless-commits 7a85788\n\nWith this trick under your belt, you can jingle around in history as much as you\u2019d like. It\u2019s not like sliding around on a timeline though. When you checkout a specific commit, you will only have access to the history from that point backwards in time. If you want to move forward in history, you\u2019ll need to move back to the branch tip by checking out the branch again.\n\n$ git checkout helpful-boss-branch\n\nYou\u2019re now back to the present. Your HEAD is now pointing to the endpoint of a known branch, and so it is no longer detached. Any changes you made while on your adventure are safely stored in a new branch, assuming you\u2019ve followed the instructions Git gave you. That wasn\u2019t so scary after all, now, was it?\n\nBack to our reindeer problem.\n\nIf your boss is anything like the bosses I\u2019ve worked with, chances are very good that at least some of their work is worth salvaging. Depending on how your repository is structured, you\u2019ll want to capture the good work using one of several different methods.\n\nBack in the living room, we\u2019ll use our bowl of nuts to illustrate how you can rescue a tiny bit of work.\n\nSaving just one commit\n\nAbout that bowl of nuts. If you\u2019re like me, you probably had some favourite kinds of nuts from an assorted collection. Walnuts were generally the most satisfying to crack open. So, instead of taking the entire bowl of nuts and dumping it into a stocking (merging the stocking and the bowl of nuts), we\u2019re just going to pick out one nut from the bowl. In Git terms, we\u2019re going to cherry-pick a commit and save it to another branch.\n\nFirst, checkout the main branch for your development work. From this branch, create a new branch where you can copy the changes into.\n\n$ git checkout master\n$ git checkout -b rescue-the-boss\n\nFrom your boss\u2019s branch, helpful-boss-branch locate the commit you want to keep.\n\n$ git log --oneline helpful-boss-branch\n\nLet\u2019s say the commit ID you want to keep is e08740b. From your rescue branch, use the command cherry-pick to copy the changes into your current branch.\n\n$ git cherry-pick e08740b\n\nIf you review the history of your current branch again, you will see you now also have the changes made in the commit in your boss\u2019s branch.\n\nAt this point you might need to make a few additional fixes to help your boss out. (You\u2019re angling for a bonus out of all this. Go the extra mile.) Once you\u2019ve made your additional changes, you\u2019ll need to add that work to the branch as well.\n\n$ git add [filename(s)]\n$ git commit -m \"Building on boss's work to improve feature X.\"\n\nGo ahead and test everything, and make sure it\u2019s perfect. You don\u2019t want to introduce your own mistakes during the rescue mission!\n\nUploading the fixed branch\n\nThe next step is to upload the new branch to the remote repository so that your boss can download it and give you a huge bonus for helping you fix their branch.\n\n$ git push -u origin rescue-the-boss\n\nCleaning up and getting back to work\n\nWith your boss rescued, and your bonus secured, you can now delete the local temporary branches.\n\n$ git branch --delete rescue-the-boss\n$ git branch --delete helpful-boss-branch\n\nAnd settle back into your chair to wait for Saint Nicholas with your book, your branch, and possibly your cat.\n\n$ git checkout waiting-for-st-nicholas\n$ git stash pop\n\nYour working directory has been returned to exactly the same state you were in at the beginning of the article.\n\nHaving fun with analogies\n\nI\u2019ve had a bit of fun with analogies in this article. But sometimes those little twists on ideas can really help someone pick up a new idea (git stash: it\u2019s like when Christmas comes around and everyone throws their fashion sense out the window and puts on a reindeer sweater for the holiday party; or git bisect: it\u2019s like trying to find that one broken light on the string of Christmas lights). It doesn\u2019t matter if the analogy isn\u2019t perfect. It\u2019s just a way to give someone a temporary hook into a concept in a way that makes the concept accessible while the learner becomes comfortable with it. As the learner\u2019s comfort increases, the analogies can drop away, making room for the technically correct definition of how something works.\n\nOr, if you\u2019re like me, you can choose to never grow old and just keep mucking about in the analogies. I\u2019d argue it\u2019s a lot more fun to play with a string of Christmas lights and some holiday cheer than a directed acyclic graph anyway.", "year": "2014", "author": "Emma Jane Westby", "author_slug": "emmajanewestby", "published": "2014-12-02T00:00:00+00:00", "url": "https://24ways.org/2014/dealing-with-emergencies-in-git/", "topic": "code"}