Paths and directory trees

Problem

What becomes confusing, fragile, or impossible without understanding paths and directory trees? 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

Paths and directory trees belongs to “Files are the first database”. A file is named bytes plus filesystem metadata; text exists only after decoding. This lesson turns paths and directory trees into a working part of weekly fixture.

For paths and directory trees, 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: Build paths and directory trees around this exact fixture: Create notes/hello.txt containing ASCII A, UTF-8 é, and 🙂 on separate lines.

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: Add paths and directory trees support for weekly boundary case: Compare composed é with decomposed e + combining acute accent.
4. Failure case: Make paths and directory trees surface—not hide—this failure: Create one lone ff byte and attempt UTF-8 decoding.

RESULT
paths and directory trees handles baseline and boundary while preserving this observable result: Valid sample is 10 bytes; composed and decomposed text look similar but have different bytes; ff is invalid UTF-8. 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: paths and directory trees' > "$lab/input.txt"
printf 'bytes: ' && wc -c < "$lab/input.txt"
od -An -tx1 -c "$lab/input.txt"

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

Independent exercise

Add one real case: paths and directory trees

1. Create second case from blank file: Add paths and directory trees support for weekly boundary case: Compare composed é with decomposed e + combining acute accent.
2. Then create controlled failure: Make paths and directory trees surface—not hide—this failure: Create one lone ff byte and attempt UTF-8 decoding.
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

• paths and directory trees handles baseline and boundary while preserving this observable result: Valid sample is 10 bytes; composed and decomposed text look similar but have different bytes; ff is invalid UTF-8.
• Command exits 0, prints a byte count, then prints hexadecimal and character views of the same file.
• Controlled paths and directory trees failure produces captured evidence; repair restores stated invariant without hiding error.

Hints

Solution

Attempt both exercises before opening reference approach.