Networking · Lesson 10 of 26 · 8 minutes

Port inventory text

Normalize and count port inventory text.

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learner@clairos:~ $

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Your objectives

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1
Unique ports
Run cat 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 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.
2
Count port entries
Run wc -l data/ports.txt.
Hint & worked example
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.
```
wc -l data/ports.txt
```
Remember: Text without a final newline may have fewer counted lines than visible rows.
3
Tail port list
Run tail -n 3 data/ports.txt.
Hint & worked example
Show the end of an input; -n selects the number of lines.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
tail -n 3 data/ports.txt
```
Remember: This browser lab snapshots output; it does not keep a live tail -f stream.

Understand the pattern

Junior operators build confidence by gathering evidence before changing systems.

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.
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.
tail: Show the end of an input; -n selects the number of lines.
This browser lab snapshots output; it does not keep a live tail -f stream.

Worked example and expected result

$ cat data/ports.txt | sort | uniq

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

$ wc -l data/ports.txt

5 data/ports.txt

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

$ tail -n 3 data/ports.txt

443
23
22

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 “Port inventory text”, which interpretation is safe?Text without a final newline may have fewer counted lines than visible rows.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 wc workflow from “Port inventory text” 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.

Next: Network log grep Try an incident drill

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