`git diff` paid off the first time I spotted a change I didn't remember making, a password field I'd meant to leave alone. This is the command that saved me from my own tired afternoons.
About 2 min of reading
Before this new lesson, one small question about the lesson you just finished. Recall it, do not look it up.
The command that caught me committing changes I did not remember making. Let me edit a file, stage part of it, and see exactly what each view is showing me before I hit enter.
Set up two files and change only one. git diff reads two versions of the project and prints every line that separates them. Right now nothing is staged, so the whole change is uncommitted, git diff shows it.
Before you run it, say out loud what it will print. Then open the answer.
Run the command you reach for before staging anything. It prints only changes not yet staged, green-plus lines are additions, red-minus lines are removals. It is the last thing you look at before touching a file you are about to save.
Before you run it, say out loud what it will print. Then open the answer.
Stage the change, then ask what is in the box. git diff --staged compares the staging area against the last commit, so it shows exactly what you are about to seal in. That is the last glance before git commit.
Before you run it, say out loud what it will print. Then open the answer.
Compare two points in history instead of two working states. HEAD is the latest commit; HEAD~1 is the one before it. The diff between them shows what that last commit actually changed.
Before you run it, say out loud what it will print. Then open the answer.
Squeeze the diff into a readable summary. --stat prints a short list of files and how many lines changed in each instead of the full patch. It is enough to see which files a commit touched without reading every line.
Before you run it, say out loud what it will print. Then open the answer.
Before you write anything, put these lines back in the right order. Click a line to move it up one step. This support step is easier than writing code from scratch, and it is here to make the last example stick.
A diff is a line-by-line comparison:
- old line of text
+ new line of textLines starting with - were deleted, + were added, and the unmarked lines in between are unchanged context so you can see what the change is about. The + and - are not git being cruel, they are the fastest way to see the shape of a change at a glance.
| Command | Shows |
|---|---|
git diff | working folder vs staging |
git diff --staged | staging vs last commit |
git diff HEAD~1 | last commit vs this one |
Most of the time git diff is the right one. Reach for the others when you need a narrower or wider view.
git diffThis prints every change you have made that is not staged yet. Green-plus lines are additions; red-minus lines are removals. Run it right before you stage anything, and you stop accidentally committing stray edits.
git diff --stagedAfter you run git add, this shows exactly what is in your staging box compared to the last commit. Last glance before git commit. I run it almost every time, and it has caught more surprises than I care to admit.
git diff HEAD~2 HEADHEAD is your latest commit. HEAD~2 is two commits back. This shows everything that changed across that window. The ~ counts parents going back, so HEAD~1 is the previous commit and HEAD~3 is three back.
Each one is defined here on this site. Open the entry for the full definition and the other words it points at.