Text and logs · Lesson 6 of 38 · 7 minutes

Case-insensitive search

Find text regardless of capitalization.

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Your objectives

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1
Search failed
Run grep -i 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 -i denied /var/log/auth.log
```
Remember: No matches is exit status 1, which is different from a malformed invocation.
2
Search root
Run grep root /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 root /var/log/auth.log
```
Remember: No matches is exit status 1, which is different from a malformed invocation.
3
Count auth log
Run wc -l /var/log/auth.log.
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 /var/log/auth.log
```
Remember: Text without a final newline may have fewer counted lines than visible rows.

Understand the pattern

Log sources do not always use consistent casing.

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.
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

$ grep -i 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 root /var/log/auth.log

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

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

$ wc -l /var/log/auth.log

3 /var/log/auth.log

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 “Case-insensitive search”, 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 “Case-insensitive search” 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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