Shell scripting · Lesson 30 of 31 · 8 minutes

Script change review

Compare configuration snapshots and record a review marker.

Open the lab Course map

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learner@clairos:~ $

↑ history · Tab complete · Ctrl+C cancel · Esc, Tab to leaveExit 0

Your objectives

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1
Review config differences
Run diff data/config-a.conf data/config-b.conf.
Hint & worked example
Compare two text files; a difference is a meaningful nonzero status, not necessarily an execution error.
Inspect the differences. diff exits 1 when files differ and 0 when they match.
```
diff data/config-a.conf data/config-b.conf
```
Remember: Status 1 means differences for diff; shell status must be interpreted in command context.
2
Identify the changed listener
Run grep listen data/config-b.conf.
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 listen data/config-b.conf
```
Remember: No matches is exit status 1, which is different from a malformed invocation.
3
Record the review
Run printf script-change-reviewed | tee lab/script-change.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 script-change-reviewed | tee lab/script-change.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.

Understand the pattern

Reviewing change evidence before script-driven deployment helps operators explain what they know before they change anything.

diff: Compare two text files; a difference is a meaningful nonzero status, not necessarily an execution error.
Status 1 means differences for diff; shell status must be interpreted in command context.
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.

Worked example and expected result

$ diff data/config-a.conf data/config-b.conf

--- /home/learner/data/config-a.conf
+++ /home/learner/data/config-b.conf
-listen 443 ssl;
+listen 8443 ssl;

Exit status: 1. This nonzero result is an expected part of this exercise.

$ grep listen data/config-b.conf

listen 8443 ssl;

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

$ printf script-change-reviewed | tee lab/script-change.txt

script-change-reviewed

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

Apply it elsewhere

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

Keep the momentum.

Complete the lab, then explain and apply the pattern.

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