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Retrieving old versions

From: Git Essential Training

Video: Retrieving old versions

In the previous movie we saw how we can use the amend option with commit in order to edit our very last commit, the commit that the HEAD still points to. We also saw how it's difficult to amend older commits, because that would violate the data integrity, which is an important feature of Git. Instead, if we need to make changes to those older commits, the best advice is to make new commits, commits that undo what was done in those older commits. Not only does it maintain the data integrity of Git, but then the log file also accurately reflects the changes that were made over time, and it shows that a 1.1 change was made and then several commits later another commit was made.

Retrieving old versions

In the previous movie we saw how we can use the amend option with commit in order to edit our very last commit, the commit that the HEAD still points to. We also saw how it's difficult to amend older commits, because that would violate the data integrity, which is an important feature of Git. Instead, if we need to make changes to those older commits, the best advice is to make new commits, commits that undo what was done in those older commits. Not only does it maintain the data integrity of Git, but then the log file also accurately reflects the changes that were made over time, and it shows that a 1.1 change was made and then several commits later another commit was made.

That information might actually have some importance, especially if the commits in between played off of those changes in any way. Now, what it doesn't do is allow us to hide our mistakes. Instead, you'll just have to record the mistake you made and then record the fix that goes with it. In order to make new commits that undo changes, there's a number of different ways that we could do it, one would be we could simply manually make those changes just like we did the first time and then commit the result. But I want to show you another way that we can do it that's a little bit faster too.

Let's take a look at our git log, and let's take a look at this last commit that we made. Now we could use amend to just edit this commit. But this is the one where we change our resources.html file. We rearrange the items that we're going to list there. Let's say we made two or three more commit since then and we wanted to go back and we wanted to rework this file and get it back to its old state. What we can do is we can check out this file, check out the old version of resources.html from before you made that change.

So, if the change was made in this commit, then the commit that has the version previous to that is this version, and probably all the versions that are before. But we'll take the one that's immediately before. And what I'm going to do is I'm going to copy part of this S-H-A at the top. Now, you could take the whole thing, but it's not necessary, these numbers are unique enough that you can usually just grab the first 10 or so characters and copy those and use those for a reference. And then I'm going to say git checkout, I'm going to use that reference to the commit that I want followed by a dash, dash, that's that bare double dash that we used before with checkout to let it know that we're not talking about a branch, we mean the current branch, and then the file that I mean, resources.html.

So now I've told it to check that out. Let's take a look at git status, and you'll see that it moved it into my index. So I've checked it out and here it is ready to be committed. Now, this behavior is slightly different. Before when I did a check out, it put up my working directory. Here it went ahead and put up my staging index. When you check it out from our particular revision, it puts it into your staging area. Now, if we do git diff --staged, we can see the comparison, and we can see that this is the old file, the old version, and if we were to commit it, it would revert those changes.

It would change it so that sunglasses, sunscreen, insect repellent move from the top back down to the bottom where they were originally. So there it is ready to be committed, I can just do a regular commit now, and it will undo that change that I made previously. It's a good habit when you're reverting a particular commit to actually refer to the SHA for that commit. So, it would be a good idea to take part of the SHA and copy it and then say this commit reverts commit, and give that SHA, so it's a reference.

So people can look it up and figure out what you were trying to revert. We could go ahead and commit that, but I'm going to instead bring up the status again. Let's do git reset HEAD on resources.html. That will put it back in our working directory, and then we'll do git check out -- resources.html, and that now removes it from our working directory so that now our working directory is clean. And the reason I don't want to do it here is because in the next movie, I'm going to show you how we can use a command called git revert to do something very similar.

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This video is part of

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Git Essential Training

89 video lessons · 32024 viewers

Kevin Skoglund
Author

 
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  1. 2m 46s
    1. Introduction
      1m 7s
    2. How to use the exercise files
      1m 39s
  2. 20m 24s
    1. Understanding version control
      4m 48s
    2. The history of Git
      7m 58s
    3. About distributed version control
      5m 4s
    4. Who should use Git?
      2m 34s
  3. 26m 12s
    1. Installing Git on a Mac
      3m 44s
    2. Installing Git on Windows
      5m 37s
    3. Installing Git on Linux
      1m 30s
    4. Configuring Git
      7m 29s
    5. Exploring Git auto-completion
      5m 35s
    6. Using Git help
      2m 17s
  4. 15m 49s
    1. Initializing a repository
      1m 58s
    2. Understanding where Git files are stored
      2m 34s
    3. Performing your first commit
      2m 4s
    4. Writing commit messages
      5m 22s
    5. Viewing the commit log
      3m 51s
  5. 17m 44s
    1. Exploring the three-trees architecture
      3m 57s
    2. The Git workflow
      3m 15s
    3. Using hash values (SHA-1)
      4m 7s
    4. Working with the HEAD pointer
      6m 25s
  6. 25m 52s
    1. Adding files
      5m 59s
    2. Editing files
      3m 56s
    3. Viewing changes with diff
      3m 35s
    4. Viewing only staged changes
      2m 28s
    5. Deleting files
      5m 29s
    6. Moving and renaming files
      4m 25s
  7. 19m 18s
    1. Introducing the Explore California web site
      2m 2s
    2. Initializing Git
      3m 48s
    3. Editing the support phone number
      6m 20s
    4. Editing the backpack file name and links
      7m 8s
  8. 38m 45s
    1. Undoing working directory changes
      3m 49s
    2. Unstaging files
      2m 37s
    3. Amending commits
      4m 50s
    4. Retrieving old versions
      4m 7s
    5. Reverting a commit
      3m 12s
    6. Using reset to undo commits
      3m 44s
    7. Demonstrating a soft reset
      4m 8s
    8. Demonstrating a mixed reset
      4m 7s
    9. Demonstrating a hard reset
      5m 8s
    10. Removing untracked files
      3m 3s
  9. 27m 22s
    1. Using .gitignore files
      8m 23s
    2. Understanding what to ignore
      4m 47s
    3. Ignoring files globally
      4m 49s
    4. Ignoring tracked files
      5m 26s
    5. Tracking empty directories
      3m 57s
  10. 26m 51s
    1. Referencing commits
      4m 52s
    2. Exploring tree listings
      3m 46s
    3. Getting more from the commit log
      7m 38s
    4. Viewing commits
      4m 4s
    5. Comparing commits
      6m 31s
  11. 39m 35s
    1. Branching overview
      4m 56s
    2. Viewing and creating branches
      2m 57s
    3. Switching branches
      2m 58s
    4. Creating and switching branches
      4m 53s
    5. Switching branches with uncommitted changes
      3m 26s
    6. Comparing branches
      4m 28s
    7. Renaming branches
      2m 28s
    8. Deleting branches
      4m 18s
    9. Configuring the command prompt to show the branch
      9m 11s
  12. 28m 32s
    1. Merging code
      3m 11s
    2. Using fast-forward merge vs. true merge
      6m 49s
    3. Merging conflicts
      7m 26s
    4. Resolving merge conflicts
      7m 5s
    5. Exploring strategies to reduce merge conflicts
      4m 1s
  13. 14m 34s
    1. Saving changes in the stash
      4m 5s
    2. Viewing stashed changes
      2m 39s
    3. Retrieving stashed changes
      4m 24s
    4. Deleting stashed changes
      3m 26s
  14. 1h 5m
    1. Using local and remote repositories
      6m 38s
    2. Setting up a GitHub account
      5m 39s
    3. Adding a remote repository
      4m 0s
    4. Creating a remote branch
      4m 3s
    5. Cloning a remote repository
      4m 26s
    6. Tracking remote branches
      4m 5s
    7. Pushing changes to a remote repository
      5m 8s
    8. Fetching changes from a remote repository
      5m 47s
    9. Merging in fetched changes
      4m 50s
    10. Checking out remote branches
      3m 22s
    11. Pushing to an updated remote branch
      2m 6s
    12. Deleting a remote branch
      3m 8s
    13. Enabling collaboration
      3m 40s
    14. A collaboration workflow
      8m 43s
  15. 16m 23s
    1. Setting up aliases for common commands
      5m 14s
    2. Using SSH keys for remote login
      2m 56s
    3. Exploring integrated development environments
      1m 4s
    4. Exploring graphical user interfaces
      4m 32s
    5. Understanding Git hosting
      2m 37s
  16. 55s
    1. Goodbye
      55s

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