title = Update files in the index
cards = add commit

[description]

When we change files, the index won't change on its own. We have to use `git add` to update the index to the changed version of the file.

Let's try that!

The icons in the file browser show you when the actual file (white) and the version in the index (blue) are different, and when they are the same!

[win]

Good! The index is sometimes also called the "staging area" - it contains exactly what ends up in the next commit when you use `git commit`!

[setup]

echo "The candle is burning with a blue flame." > candle
git add .
git commit -m "The beginning"

[win]

# Make a change to the candle.
test "$(git diff --name-only)" = "candle" || file -f .git/candle-changed && touch .git/candle-changed

# Add the candle.
test "$(git diff --cached --name-only)" = "candle" || file -f .git/candle-added && touch .git/candle-added

# Make a commit.
test "$(git diff --name-only HEAD HEAD^)" = "candle"
