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Viewing changes with diff

From: Git Essential Training

Video: Viewing changes with diff

In the last movie we saw how we could edit files and commit those to the repository. In this movie I'd like us to take a look at how we can see what changes have been made before we make a decision about whether to commit those to the repository. Before we begin that, let's make some edits. So let's open up our first_file.txt, and this is the first file added to my project, and I'm going to say space, it comes before all other files. Hit Return. I'll save the whole thing, close it up. Now, we know what's going to happen if we do git status, it's going to tell us that the file was modified, right? What we want to do now though is find out what were those modifications.

Viewing changes with diff

In the last movie we saw how we could edit files and commit those to the repository. In this movie I'd like us to take a look at how we can see what changes have been made before we make a decision about whether to commit those to the repository. Before we begin that, let's make some edits. So let's open up our first_file.txt, and this is the first file added to my project, and I'm going to say space, it comes before all other files. Hit Return. I'll save the whole thing, close it up. Now, we know what's going to happen if we do git status, it's going to tell us that the file was modified, right? What we want to do now though is find out what were those modifications.

This is very useful, especially if we've been working for a couple of hours, we've been making lots of changes to lots of files in our project, and maybe we were a little surprised even to see that the file popped up here in the modified list, we don't remember making a change to that file. How can we refresh our memory? What changed about this file? In the UNIX world it's very common to use a program called diff, D-I-F-F, in order to compare two files. And so Git uses that as the term that it uses to show us a diff between the old version and the new version. And we do that just with git diff.

So git diff will compare the two, that's comparing what's in the repository, the version that HEAD is pointing at, versus what's in our working directory. So the version in the repository is the one with the minuses, the one that has the pluses is going to be what's in the new version. So the old version was, this is the first line that I added to my project. The new version replaced that line with this line, this is the first file added to my project, and added two more new lines, it comes before all other files. Of course, what I changed here was just this little bit of text, it doesn't tell us that, it tells us on a line by line basis what is different.

It also notes that there's no new line at the end of this file, which means that we don't have a line return after the period. We do have a line return after this one here. So you can kind of ignore this line, don't worry too much about it. Main thing that you want to see is that this line has been removed, this line has been added, as well as these two lines have been added, that's what it's telling us. Now, if we'd had a long document, let's say it was 300 lines long, it would just highlight just the little bit that had changed. It wouldn't show us the whole document, it would just say, oh, you know what, this is the bit that's changed, and this little bit right here would actually tell us what line numbers we were looking at. That's a subtle but important point.

In most text editors there is a way to view line numbers. For example, in TextMate, under the View Menu, in the Gutter, I can tell it to show me line numbers. Then it will show the line numbers out here, and that will help you locate these changes relative to what's being told to you in the diff file. Now, if we'd had changes to more than one file, let's take a look here, let's open up a third file, and we'll just say, This is the last file in the project right now. Save that, come back over here, and let's take a look at git diff again.

And you'll see that it tells me, here is the changes in first file, here's the changes in third file, it lists them one after the other. If I wanted just one of those, of course, git diff with first_file.txt would just report the changes to that single file. So we can see all of the changes that have been made, that's all of the changes listed here under modified, or we can go file by file and take a peek at each one of them. Now, when we do this we're looking at the difference between the repository version and our working directory.

In the next movie let's look at how we see the changes that are in our staging directory.

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This video is part of

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Git Essential Training

89 video lessons · 31830 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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