leejunkim

Git diff

3 min read

Not critical/fundamental, but very useful!

  • Helps us view between different things we can compare in a repo (commands, branches, files, areas, etc)
  • We often use git diff alongside commands like git status and git log, to get a better picture of a repo and how it has changed over time
    • doesn’t impact anything, just a purely INFORMATIVE COMMAND
  • Useful when:
    • You made a BUNCH of changes and you don’t remember what you did lmao
  • Compares Staging Area and Working Directory

Reading the output of git diff

  • git diff
    • lists all the changes in our working directory that are NOT staged for the next commit
  • Let’s say we have new changes (added indigo and violet) that are not added
  • Then when we git diff, we get this:
    • diff --git a/rainbow.txt b/rainbow.txt → files to be compared
      • usually the same file, just 2 versions (git declares one file as A and the other as `B)
    • index 72d1d5a..f2c8117 100644
      • metadata (just ignore it)
    • --- a/rainbow.txt and +++ b/rainbow.txt
      • They get assigned each a symbol
      • --- a/rainbow.txt: For file a, changes will be indicated with -
      • +++ b/rainbow.txt: For file b, changes will be indicated with +
    • The rest
      • You can see a little bit of context before and after the change
      • The header: @@ -3,4 +3,5 @@
        • From file a, 4 lines are extracted (as a chunk) starting from line 3
        • From file b, 5 lines are extracted starting from line 3
      • orange there is just lie 2 lol

git diff VS git diff --cached VS git diff HEAD

  • git diff
    • This will show the difference between your working directory (which has the new change) and the staging area (which doesn’t have the new change).
    • only shows changes in tracked files
      • New files that haven’t been added to Git yet are considered untracked
  • See git workflow
The differences
  • git diff shows what’s not yet staged
  • git diff HEAD shows all modifications, regardless of staging
  • git diff --cached shows what’s staged and ready to be committed
Example
  • Scenario
    • Start with a clean state (everything committed)
    • Modify file A and stage it
    • Modify file B but don’t stage it
  • The commands
    • git diff will show only changes in file B (unstaged changes)
    • git diff HEAD will show changes in both file A and B (all changes since last commit)
    • git diff --cached will show only changes in file A (staged changes)
JUST REMEMBER THIS
  • What changes are you still working on? (git diff)
  • What added changes are ready to be committed? (git diff —cached)
  • What’s the total set of changes you’ve made? (git diff HEAD)

Using a GUI

Using a GUI shines in applications like this

  • Example
  • Showing diff in 2 commits - Just press shift

Graph View

Backlinks