Lesson 2.5.3: History and going back

What you save with Git can be looked at and recovered: the history, the changes and any earlier version.

The idea

Saving versions only helps if you can look at them and get them back. Three commands:

git log: the list of commits.
git diff: what you've changed since the last one.
git restore: going back.

The history

Terminal

$ git log --oneline

Terminal

7b1e0d4 (HEAD -> main) Add the 3 times table
3f2a1c9 Add the greeting

Each commit has an identifier: 7b1e0d4.
The most recent is at the top.
HEAD marks where you are.

If the list doesn't fit, Git shows it page by page: the q key gets you out.

What you've changed

Change the text in hello.js to "Goodbye from a file", save, and:

Terminal

$ git diff

Terminal

diff --git a/hello.js b/hello.js
index 5c1b2a3..8d4e6f1 100644
--- a/hello.js
+++ b/hello.js
@@ -1 +1 @@
-console.log("Hello from a file");
+console.log("Goodbye from a file");

What matters are the last lines: with -, what goes out; with +, what comes in.

Undoing what you haven't saved

Terminal

$ git restore hello.js

The file goes back to how it was in the last commit.

Careful: whatever wasn't in a commit is lost, and this can't be undone.

Getting an old version back

With a commit's identifier, bring the file back as it was then:

Terminal

$ git restore --source=3f2a1c9 hello.js

The file changes in your folder. If you want to keep that version, make a commit.

Try it

Exercise

Delete everything in table.js and save. Look at the change with git diff and get the file back.

Show the solution

Terminal

$ git diff
$ git restore table.js
$ git status

git diff shows every line with -. After git restore, git status says nothing to commit again.

Summary

git log --oneline shows the history; each commit has an identifier.
git diff shows what changed: - out, + in.
git restore file throws away unsaved changes, for good.
git restore --source=id file brings back an old version.