World 10: Deep Git

Revision syntax

You will learn: how to name any commit, or a group of commits, without copying ids.

The problem

~/shop $ git log --oneline --graph --all* c804c3f (HEAD -> main) Add about page| * 9cd9e6c (prices) Add a price|/  * ab7c243 Link the menu*   ec4a356 Merge menu|\  | * bdfdf02 (menu) Add onde-onde| * 4a73658 Add menu page* | ce13150 Say we open daily|/  * dd18cc9 Add shop page

You need the commit two steps back. Copying long ids gets old fast. Is there a shorter way?

Watch

A is any way to name a commit. HEAD~2 means two steps back from HEAD. Each step follows the first parent.

Try it

Count the steps back along main.

Tap the commit that HEAD~3 names.

Hint

The merge has two parents. ~ always takes the first one, on main.

Predict

HEAD~2 is a merge, so it has two parents. ^2 picks the second one. Which commit is HEAD~2^2?

Try it

Visit “Add menu page” with git switch --detach. Name it from HEAD, using ~ and ^.

Hint

Start from HEAD~2^2. Then go one more step back.

Watch

~/shop $ git log --oneline main..prices9cd9e6c (prices) Add a price~/shop $ git log --oneline prices..mainc804c3f (HEAD -> main) Add about page

A..B (two dots) lists commits in B that A does not have. Swap the sides, and you see the other side’s extra work.

Try it

A...B (three dots) lists commits on either side, but not both. --left-right marks the sides: < for A, > for B.

Tap the commit that only prices has.

~/shop $ git log --oneline --left-right main...prices

0 of 1 found

Check

Before a merge, you review what prices will bring into main. Which command?

You did it!

You can now name any commit without copying its id.

Go deeper (optional)

HEAD^ is the same as HEAD~1. HEAD@{1} is where HEAD was one move ago, from the reflog. v1.0^{} is the commit a tag points to. git rev-parse turns any revision into a full id. git diff main...prices shows what prices changed since it split off.

~/shop $ git rev-parse --short HEAD~2^2bdfdf02~/shop $ git diff main...pricesdiff --git a/menu.html b/menu.htmlindex d80e4d9..b83048a 100644--- a/menu.html+++ b/menu.html@@ -1,3 +1,3 @@ <h1>Menu</h1>-<p>Kuih lapis</p>+<p>Kuih lapis RM1</p> <p>Onde-onde</p>