Text and logs · Lesson 4 of 38 · 9 minutes

Text pipelines

Use safe simulated pipes to count, sort, and deduplicate text output.

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Your objectives

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1
Count piped words
Run echo alpha beta beta | wc.
Hint & worked example
Write simple text to standard output. Prefer printf when exact formatting matters. Count input. -l counts newline characters, -w counts whitespace-delimited words, and -c counts bytes.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
echo alpha beta beta | wc
```
Remember: Redirection can overwrite an existing file before the command runs. Text without a final newline may have fewer counted lines than visible rows.
2
Sort and dedupe
Run cat /home/learner/data/ports.txt | sort | uniq.
Hint & worked example
Read one or more files to standard output without editing their contents. Order lines before comparing or grouping them; -n compares numerically and -r reverses order. Collapse adjacent duplicate lines; use sort first when duplicates are not already together.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
cat /home/learner/data/ports.txt | sort | uniq
```
Remember: Reading a source file should precede changing it; avoid printing real secrets. Alphabetical sorting is not numeric sorting. uniq does not find every duplicate in an unsorted stream.
3
Write a safe note
Run echo pipeline-practice > lab-pipeline.txt.
Hint & worked example
Write simple text to standard output. Prefer printf when exact formatting matters.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
echo pipeline-practice > lab-pipeline.txt
```
Remember: Redirection can overwrite an existing file before the command runs.

Understand the pattern

Pipelines make terminals powerful, but this lab keeps them tightly limited.

echo: Write simple text to standard output. Prefer printf when exact formatting matters.
Redirection can overwrite an existing file before the command runs.
wc: Count input. -l counts newline characters, -w counts whitespace-delimited words, and -c counts bytes.
Text without a final newline may have fewer counted lines than visible rows.
cat: Read one or more files to standard output without editing their contents.
Reading a source file should precede changing it; avoid printing real secrets.
sort: Order lines before comparing or grouping them; -n compares numerically and -r reverses order.
Alphabetical sorting is not numeric sorting.
uniq: Collapse adjacent duplicate lines; use sort first when duplicates are not already together.
uniq does not find every duplicate in an unsorted stream.

Worked example and expected result

$ echo alpha beta beta | wc

1 3 16

Exit status: 0. The command completed successfully in the training fixture.

$ cat /home/learner/data/ports.txt | sort | uniq

Exit status: 0. The command completed successfully in the training fixture.

$ echo pipeline-practice > lab-pipeline.txt

(no output; exit 0)

Exit status: 0. The command completed successfully in the training fixture.

Try a variation

Repeat this workflow in the sandbox with a different scratch filename. Keep the system fixtures unchanged and compare the observed output with your expectation before moving on.

Explain it

In “Text pipelines”, which interpretation is safe?Reading a source file should precede changing it; avoid printing real secrets.A command appearing in history proves it completed successfully.A successful first check guarantees that every dependent service is healthy.

Apply it elsewhere

Before adapting the cat workflow from “Text pipelines” to another server, what should you do?Paste the training paths unchanged into production.Skip output inspection whenever the command is familiar.Confirm the current directory, target identity, permissions, and the installed command behavior first.

Keep the momentum.

Complete the lab, then explain and apply the pattern.

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