Text and logs · Lesson 2 of 38 · 8 minutes

Grep practice

Search literal text in logs and practice case-insensitive matching.

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learner@clairos:~ $

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

Your objectives

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1
Find denied auth
Run grep denied /var/log/auth.log.
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 denied /var/log/auth.log
```
Remember: No matches is exit status 1, which is different from a malformed invocation.
2
Search nginx case-insensitively
Run grep -i nginx /var/log/syslog.
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 -i nginx /var/log/syslog
```
Remember: No matches is exit status 1, which is different from a malformed invocation.
3
Search config text
Run grep server_name /etc/nginx/sites-available/learn.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 /etc/nginx/sites-available/learn.conf
```
Remember: No matches is exit status 1, which is different from a malformed invocation.

Understand the pattern

Fast text search is one of the most valuable terminal habits.

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

$ grep denied /var/log/auth.log

May 26 08:18:33 clairos-learn sshd[118]: denied password for root
May 26 08:21:44 clairos-learn sshd[141]: denied password for admin

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

$ grep -i nginx /var/log/syslog

May 26 08:10:00 clairos-learn systemd: Started fake nginx

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

$ grep server_name /etc/nginx/sites-available/learn.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 “Grep practice”, 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 “Grep practice” 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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