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Digital · Guided lesson

Rerun with a changed input and hand off

About 36 minutes · 6 reading + 30 practice and checks
Time includes reading, practice, and questions. Extra videos or further study are optional.
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A repeatable Bash workflow with checked registration counts, a controlled rerun and clear handoff instructions.

Keep your working files in your own notebook or software. Save a private description, checklist, and work link in My Proof.

What to include

  • Location and path log.
  • Raw-row count with header handling.
  • Confirmed counts by session.
  • Reviewed script and dedicated output path.
  • Baseline/variation results and handoff.

Review and revise

Use these criteria to check your work and choose what to improve.

  • Paths and quoting are accurate.
  • Counts reconcile with the fixture.
  • Raw data is preserved.
  • Rerun and limitations are explained.
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Before you begin

The idea in everyday life

Summarize fictional workshop registrations using Bash and a small tab-separated file.

The idea

A repeatable workflow must handle both the original input and a documented variation.

Follow along

Rerun with a changed input and hand off — guided practice

Verify that the script responds predictably to a controlled data change.

Create an empty shell-lab folder. Inside it create input and output folders. Put registrations.tsv in input with these tab-separated rows and a final newline: session<TAB>status; art<TAB>confirmed; code<TAB>confirmed; art<TAB>waiting; code<TAB>confirmed; music<TAB>confirmed. Start the terminal in shell-lab. Bash required; no sudo, remote systems or deletion commands. First restore the original supplied file if an earlier variation changed it. Run summarize.sh once to establish the base output.

  1. 1. Record the baseline

    Write art=1, code=2, music=1 and total=4 in run-log.md.

    You should see: The baseline matches the original five data rows.

    A baseline makes later changes interpretable.

  2. 2. Change one record

    Append a tab-separated music confirmed row, with a final newline, to the input file in a text editor.

    You should see: There are six data rows, five confirmed.

    One controlled change gives a predictable expected effect.

  3. 3. Rerun

    Run the script and inspect its output.

    bash summarize.sh
cat output/confirmed.txt

    You should see: Music increases to 2; art and code remain 1 and 2.

    A focused difference checks that the workflow responds to data.

  4. 4. Hand off

    Complete run-log.md with Bash requirement, launch command, paths, original/changed totals and fixture limitation.

    You should see: Another learner can restore the original and reproduce both runs.

    A command without data assumptions is an incomplete handoff.

Now change one thing

From the original four confirmed rows, add two confirmed rows and one waiting row. What confirmed total should result?

Your work

What to finish

A script, input, two run records and clear operating instructions.

Common mistake

Watch for this

Forgetting to reset the input makes repeated variations accumulate and invalidates expected totals.

How can I tell I understand it?

Complete the changed case, explain your result, and pass the three application checks.

Try 3 questions

Quick knowledge check

Answer all 3 questions. Get at least 2 right and the lesson completes automatically.

Not yet passed

You’ll get an explanation for each answer. Signed in? Your results save to your account.

1A changed run adds one waiting row and the confirmed total rises. What should you investigate?
2The baseline has 7 confirmed rows; three confirmed rows are added. Expected total?
3The report contains another copy of the results after every rerun despite unchanged input. What is a likely cause?
0 of 3 answeredApply the lesson to a short question, then review the explanation.
6
Finish this lesson

Pass the check. We’ll save the progress.

Answer all 3 questions above and get at least 2 right. You can review the explanations and try again.

Go to the knowledge check
Optional course overview video · same video as Lesson 1
Missing SemesterLecture 1: Course Overview + The Shell (2020)YouTube
Optional course overview

Lecture 1: Course Overview + The Shell (2020)

From Missing Semester. Watch here or open it on YouTube .

Optional course overview. Follow the written steps below at your own pace.
Tools, templates, and lesson sources

Tools and templates

Tools open in a new tab so you can keep your place here.

Sources and further reading

Explore the references behind this lesson.

Software Carpentry: Navigating Files and Directories
Source & access notes · checked 2026-09-12

Opened and inspected on 2026-09-12: Working directory and relative paths.

Access: Free public web page; no paid enrollment required.

Reuse: CC BY 4.0 instruction; MIT examples. Independent fixture used.

Software Carpentry: Pipes and Filters
Source & access notes · checked 2026-09-12

Opened and inspected on 2026-09-12: Sorting, counts, pipes and redirection.

Access: Free public web page; no paid enrollment required.

Reuse: CC BY 4.0 instruction; MIT examples. Independent fixture used.

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