Shell scripting · Lesson 8 of 31 · 8 minutes

Cut in scripts

Extract account fields for script-style checks.

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Your objectives

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1
Capture users
Run cut -d : -f 1 /etc/passwd | tee lab/users.txt.
Hint & worked example
Extract delimiter-separated fields or character ranges from text. Copy a stream both to a file and standard output; -a appends.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
cut -d : -f 1 /etc/passwd | tee lab/users.txt
```
Remember: A delimiter parser is not a general CSV parser with quoted fields. tee can overwrite a file even though the output is also visible on screen.
2
Read users
Run cat lab/users.txt.
Hint & worked example
Read one or more files to standard output without editing their contents.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
cat lab/users.txt
```
Remember: Reading a source file should precede changing it; avoid printing real secrets.
3
Count users
Run wc -l lab/users.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 lab/users.txt
```
Remember: Text without a final newline may have fewer counted lines than visible rows.

Understand the pattern

Junior operators build confidence by gathering evidence before changing systems.

cut: Extract delimiter-separated fields or character ranges from text.
A delimiter parser is not a general CSV parser with quoted fields.
tee: Copy a stream both to a file and standard output; -a appends.
tee can overwrite a file even though the output is also visible on screen.
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.
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.

Worked example and expected result

$ cut -d : -f 1 /etc/passwd | tee lab/users.txt

root
learner
www-data

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

$ cat lab/users.txt

root
learner
www-data

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

$ wc -l lab/users.txt

3 lab/users.txt

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

Apply it elsewhere

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

Keep the momentum.

Complete the lab, then explain and apply the pattern.

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