Read history without moving HEAD

• Distinguish HEAD, a selected commit, author and committer.
• Follow parents and first-parent ancestors.
• Read two-dot/three-dot log sets without confusing them with diff endpoints.
• Compare two actual commits in GitTree without rewriting history.

You start where lesson 7 ended: main has three commits from lessons 5 to 7. Only the CSS radius remains modified: HEAD and the index hold CSS-02-INDEX, the working file CSS-02-WORKING. No remote. The video was recorded with Git 2.52.0 and GitTree 2.0 on Ubuntu 24.04: both commits, the document, the graph inspection, the search, Jump to HEAD and Compare References were operated in the app, and the terminal checks ran against what the app created, so the commit ids shown are the ones the app compared. The diverged-branch case is a diagram: no feature branch was created. Nothing was run on macOS or Windows, and Ubuntu is the only Linux system recorded. GitTree's source minimum is Git 2.39.0; once you are signed in, local inspection and commits are on the Free plan.

A commit records a tree, metadata and parent IDs. A branch names a commit; HEAD usually names the current branch. Clicking another graph row changes the app's selection, not HEAD, the branch or disk files. Author records who wrote the work; committer records who recorded this commit. They happen to be the same fictional identity here.

For a linear chain, HEAD~1 follows one first-parent edge; HEAD~2 follows two. HEAD^1 is the first parent; HEAD^2 means the second parent of one commit, not “two commits back.” A non-merge commit has no second parent.

git log A..B means reachable from B excluding reachable from A. git log A...B means symmetric difference of reachability. git diff A B compares endpoint trees, while git diff A...B compares merge-base(A,B) to B. A three-dot log and three-dot diff do not ask the same question. On this linear history some results happen to agree; do not generalize that coincidence to diverged branches. Revision notation, diff semantics.

Reading/selecting/searching changes no index, working bytes or refs. This lesson's two explicit commits do move local main: radius first, documentation second. No remote changes.

First commit the existing radius edit as shown below. Then create docs/history.md with this full UTF-8/LF body; its final item describes the commit that will contain the document, not an invented SHA.

# GitTree Features history

The first-parent chain on main, oldest first:

1. feat: add the GitTree Features hero
2. feat: add styling and local project checks
3. feat: refine the hero and card spacing
4. style: finish the card radius change
5. docs: record logs-and-revisions practice

After this document is committed, HEAD names item 5.
HEAD~1 names item 4; HEAD~2 names item 3.
Selecting a graph row does not move HEAD.
These labels are descriptions, not fabricated commit SHAs.

All identities in this project are fictional.

Do not add the optional practice notebook or extra clean-up commits to this five-commit chain.

1. Palette Show Working Changes (Command/Ctrl+Shift+P to open palette). Click styles.css under Unstaged Files. Confirm only radius 0.5rem → 0.75rem remains; do not repeat the earlier width change.
2. Choose its Stage File row action, enter Summary style: finish the card radius change, ordinary options off, then Commit Changes to 1 File (or Command/Ctrl+Enter once). Verify four commits and clean tracked status.
3. Palette New File… → Path from the project folder = docs/history.md → Create. Paste the full document and Save. Back to Graph → Show Working Changes → Stage File for docs/history.md.
4. Summary docs: record logs-and-revisions practice; commit one file. The expected chain now has five commits.
5. Click the root hero row. Inspect its real SHA, subject, author/committer and root commit parent status in commit details. Click the latest row; compare its parent relation. Do not invoke Check Out This Commit merely to read it.
6. In commit details toggle View all files to distinguish the commit's whole tree from only changed paths; inspect the document at its recorded revision. This does not modify the working file.
7. Return Back to Graph; use palette Search Loaded History or Command/Ctrl+F while the graph is active, type radius and inspect matching loaded history. In an editor the same chord finds editor text. Clear the search afterwards. A loaded-history search is not a server-wide history query.
8. Palette Jump to HEAD, Command/Ctrl+Shift+H, locates the current tip. Selection/search can move while native git symbolic-ref --short HEAD still reports main.
9. Use native git rev-parse HEAD~2 to obtain its real commit ID; no fixed course SHA is supplied. Palette Compare References… (repo.compareRefs) opens Compare References. In Old side, paste that measured ID and select its commit option; in New side, choose HEAD. The picker accepts a commit ID, not a promise that arbitrary revision expressions are parsed there.
10. Under What to compare, choose The two endpoints then Compare. Expect docs/history.md and styles.css differences for this chain. Reopen/change comparison and choose Changes since the merge base with the same sides: linear ancestry makes the endpoint result coincide here. Do not infer symmetric-log behavior from that view. Cancel exits without changing history.

Native mutation alternative, only before corresponding app success:

git add -- styles.css
git commit --quiet -m "style: finish the card radius change"

Both succeeded silently. After saving the full document:

git add -- docs/history.md
git commit --quiet -m "docs: record logs-and-revisions practice"
git log --reverse --format=%s

Full observed chain:

feat: add the GitTree Features hero
feat: add styling and local project checks
feat: refine the hero and card spacing
style: finish the card radius change
docs: record logs-and-revisions practice

Inspect set versus tree:

git log --format=%s HEAD~2..HEAD
git log --format=%s HEAD~2...HEAD

Each query separately printed:

docs: record logs-and-revisions practice
style: finish the card radius change

They coincide only because the older endpoint is an ancestor here.

git diff --name-only HEAD~2 HEAD
git rev-list --count HEAD
git symbolic-ref --short HEAD

Outputs in order:

docs/history.md
styles.css
5
main

The two named files are tree differences, not the identities of the two commits returned by log.

git rev-parse --verify --quiet HEAD^2

Observed no stdout/stderr and exit 1: latest commit is not a merge. Use HEAD~2 for two first-parent steps instead. To identify a real comparison ID:

git rev-parse HEAD~2

Read its actual output during rehearsal; a measured SHA changes with commit metadata and must not be copied from a model label.

At the end of this lesson: five commits on main in the documented order; tracked work/index clean, no remote or operation in progress. CSS now has radius 0.75rem and docs/history.md is committed. Reading a past graph row has not detached HEAD.

• Treating selected row as checked-out commit: inspect HEAD independently.
• Reading ^2 as ~2: second parent versus two first-parent edges.
• Applying symmetric-log meaning to three-dot diff: diff is directional from merge base to right.
• Assuming graph search covers unloaded/unfetched history.

A missing revision can mean insufficient ancestry, a typo or a shallow boundary, not corruption. Verify the chain and selected repository. Clear app filters before concluding a commit vanished. Do not fetch from an arbitrary provider, reset or checkout merely to repair a selection. If a document already exists, inspect its content before applying this new-file step.

Answer each question, then read why. Questions marked “Required” count toward completing the lesson.

1. Question 1 of 6

   Question 1 of 6

   Clicking an older graph row does what here?

   Choose one answer.

   Changes app selection

   Deletes newer commits

   Detaches HEAD

   Check answer
2. Question 2 of 6

   Question 2 of 6

   Which statements are correct on this five-commit linear chain?

   Choose every answer that applies.

   HEAD^2 means the second parent

   ^2 always equals ~2

   HEAD~2 follows two first-parent edges

   Check answer
3. Question 3 of 6

   Question 3 of 6Required

   Which subjects are in HEAD~2..HEAD after history.md is committed?

   Choose one answer.

   Only files named HEAD

   All five commits

   History document and radius

   Check answer
4. Question 4 of 6

   Question 4 of 6Required

   Main is H5; feature F descends from H3. What is main...feature in git log?

   Choose one answer.

   H4, H5 and F

   Only F

   Only H3

   Check answer
5. Question 5 of 6

   Question 5 of 6

   Does git diff A...B mean the symmetric log set?

   Choose one answer.

   No, merge base → B tree

   It always moves HEAD

   Yes, identical operators everywhere

   Check answer
6. Question 6 of 6

   Question 6 of 6Required

   Which observations prove the finished checkpoint?

   Choose every answer that applies.

   HEAD still main after selection

   Dirty radius still pending

   Five exact subjects in order

   Check answer

Select an older row and prove HEAD stays main. Explain why two log entries can correspond to differences in only two paths. Changed input: for a separate branch with one commit from H3 while main is at H5, predict main..feature contains only that feature commit, but main...feature also includes H4/H5. Do not create that branch in the canonical checkpoint; use a disposable copy.

• Selection and HEAD have different owners.
• Parent notation and revision sets describe ancestry, not file changes.
• Compare real resolved endpoints and label the question clearly.

• Commit the selected hunk, not the whole file (lesson 7)
• Stage the intended snapshot and make your first commit (lesson 5)
• Download GitTree

Commit — إيداع; parent — إيداع أب; ref — مرجع; revision — مراجعة; range — نطاق; merge base — أساس الدمج; author — المؤلف; committer — المُودِع.