Shell scripting · Lesson 13 of 31 · 8 minutes

Script diff review

Compare config snapshots as a script review habit.

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learner@clairos:~ $

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

Your objectives

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1
Compare configs
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
Search changed listen
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
Search server name
Run grep server_name data/config-a.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 server_name data/config-a.conf
```
Remember: No matches is exit status 1, which is different from a malformed invocation.

Understand the pattern

Junior operators build confidence by gathering evidence before changing systems.

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.

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.

$ grep server_name data/config-a.conf

server_name learn.clairos.ai;

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 diff review”, which interpretation is safe?No matches is exit status 1, which is different from a malformed invocation.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 grep workflow from “Script diff review” 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: Script checksum review Try an incident drill

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