Inspect, undo, ignore

You already know how to put files in the index and make a commit. Now you need three more things: to see what exactly changed since the last snapshot, to roll back what you did by mistake, and to tell git which files it should not notice at all.

What changed: git diff

git status answers the question "which files were touched". git diff answers "what inside them was touched, line by line".

Edit one line in report.txt and add another line at the end. Then ask git:

$ git diff
diff --git a/report.txt b/report.txt
index 98679e4..3394999 100644
--- a/report.txt
+++ b/report.txt
@@ -1,4 +1,5 @@
 Q3 report
 
-Sales grew.
+Sales grew by 12%.
 We hired two people.
+Next quarter's budget is approved.

The first