Shell scripting · Lesson 25 of 31 · 8 minutes

Shell expanded checkpoint

Complete a script review from guards to logs.

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learner@clairos:~ $

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Your objectives

Hints are always available. Wrong turns never cost XP.

1
Check deploy exists
Run test -f scripts/deploy.sh.
Hint & worked example
Evaluate a file or string condition through its exit status rather than printed output.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
test -f scripts/deploy.sh
```
Remember: A successful test usually prints nothing; inspect $? or chain a command.
2
Find strict guard
Run grep "set -eu" scripts/deploy.sh.
Hint & worked example
Select input lines that match a pattern; -i ignores case, -n adds line numbers, and -v inverts selection.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
grep "set -eu" scripts/deploy.sh
```
Remember: No matches is exit status 1, which is different from a malformed invocation.
3
Write checkpoint
Run printf shell-expanded | tee lab/shell-expanded.txt.
Hint & worked example
Format data deliberately, including separators and final newlines. 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.
```
printf shell-expanded | tee lab/shell-expanded.txt
```
Remember: A format string controls output; a newline is data, not an automatic guarantee. tee can overwrite a file even though the output is also visible on screen.
4
Inspect checkpoint
Run stat lab/shell-expanded.txt.
Hint & worked example
Inspect a file or directory metadata record, including ownership, permissions, and size.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
stat lab/shell-expanded.txt
```
Remember: Metadata and file contents answer different questions.

Understand the pattern

Junior operators build confidence by gathering evidence before changing systems.

test: Evaluate a file or string condition through its exit status rather than printed output.
A successful test usually prints nothing; inspect $? or chain a command.
grep: Select input lines that match a pattern; -i ignores case, -n adds line numbers, and -v inverts selection.
No matches is exit status 1, which is different from a malformed invocation.
printf: Format data deliberately, including separators and final newlines.
A format string controls output; a newline is data, not an automatic guarantee.
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.
stat: Inspect a file or directory metadata record, including ownership, permissions, and size.
Metadata and file contents answer different questions.

Worked example and expected result

$ test -f scripts/deploy.sh

(no output; exit 0)

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

$ grep "set -eu" scripts/deploy.sh

set -eu

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

$ printf shell-expanded | tee lab/shell-expanded.txt

shell-expanded

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

$ stat lab/shell-expanded.txt

Path: /home/learner/lab/shell-expanded.txt
Type: file
Mode: -rw-r--r--
Owner: learner
Group: learners
Size: 14 bytes

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 “Shell expanded checkpoint”, which interpretation is safe?A successful first check guarantees that every dependent service is healthy.No matches is exit status 1, which is different from a malformed invocation.A command appearing in history proves it completed successfully.

Apply it elsewhere

Before adapting the grep workflow from “Shell expanded checkpoint” 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.

Next: Script input guard Try an incident drill

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