Branching and merging

Problem

What becomes confusing, fragile, or impossible without understanding branching and merging? This lesson answers that through explanation, a worked example, two runnable exercises, and a reference solution. No teacher-supplied worksheet is required.

Before integrated development environments, the operating system, terminal, files, and text streams were the environment. Their small composable interfaces still underpin modern tooling.

Concept explanation

Branching and merging belongs to “Git as a content-addressed database”. branching and merging must be connected to layer below by tracing representation, ownership, control, and failure. Git stores immutable blobs and trees; commits point to trees and parents while refs remain movable names.

For branching and merging, trace concrete input, state transition, output, and failure through an operating-system boundary made visible through bytes, files, processes, and exit status.

Programs are processes. They read bytes, transform state, write bytes, open files and sockets, then report success or failure through observable boundaries. Apply that model to supplied normal, boundary, and failure cases; each case below names its input and expected evidence.

Example bank

Compare normal, boundary, failure, and cross-layer cases. Predict each observation before revealing the explanation.

Worked example

Start from supplied lab.sh. Focus: Trace branching and merging end-to-end while running: Commit one file, then inspect blob, tree, commit, HEAD, and index with plumbing commands.

1. Run: chmod +x lab.sh && ./lab.sh
2. Save baseline evidence. Use wc, od, stat, ps, lsof, curl, or Git plumbing as appropriate; save raw output before interpretation.
3. Boundary case: At every branching and merging boundary, label owner and representation during: Amend content with same filename and compare object IDs.
4. Failure case: Locate first layer where evidence diverges during: Detach HEAD, make a commit, move away, then recover it from reflog.

RESULT
Trace explains Changed bytes create new blob/tree/commit IDs; reflog retains recoverable commit after ref moves. without skipping any conversion, queue, process, protocol, or storage boundary. Starter-level baseline: Command exits 0, prints a byte count, then prints hexadecimal and character views of the same file.

Starter material

Create lab.sh, paste this exact content, then run the command below.

#!/usr/bin/env sh
set -eu
lab="${TMPDIR:-/tmp}/reforging-lab"
mkdir -p "$lab"
printf '%s\n' 'baseline: branching and merging' > "$lab/input.txt"
printf 'bytes: ' && wc -c < "$lab/input.txt"
od -An -tx1 -c "$lab/input.txt"

STOP / CLEANUPNo background process. Keep generated evidence files for your notebook.

Independent exercise

Remove one abstraction: branching and merging

1. Create second case from blank file: At every branching and merging boundary, label owner and representation during: Amend content with same filename and compare object IDs.
2. Then create controlled failure: Locate first layer where evidence diverges during: Detach HEAD, make a commit, move away, then recover it from reflog.
3. Use Ghostty · tmux · hx · shell · curl · Git to prove behavior, then repair controlled failure.
4. Compare result against supplied acceptance checks and reference approach before marking complete.

Expected result

• Trace explains Changed bytes create new blob/tree/commit IDs; reflog retains recoverable commit after ref moves. without skipping any conversion, queue, process, protocol, or storage boundary.
• Command exits 0, prints a byte count, then prints hexadecimal and character views of the same file.
• Controlled branching and merging failure produces captured evidence; repair restores stated invariant without hiding error.

Hints

Solution

Attempt both exercises before opening reference approach.