Terminal basics · Lesson 18 of 34 · 8 minutes

Existence checks

Use test to reason about files and directories.

Open the lab Course map

Mastery 0/3Run itExplain itApply it

learner@clairos:~ $

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

Your objectives

Hints are always available. Wrong turns never cost XP.

1
Check file
Run test -f README.txt.
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 README.txt
```
Remember: A successful test usually prints nothing; inspect $? or chain a command.
2
Check directory
Run test -d /etc.
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 -d /etc
```
Remember: A successful test usually prints nothing; inspect $? or chain a command.
3
Inspect checked file
Run stat README.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 README.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.
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 README.txt

(no output; exit 0)

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

$ test -d /etc

(no output; exit 0)

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

$ stat README.txt

Path: /home/learner/README.txt
Type: file
Mode: -rw-r--r--
Owner: learner
Group: learners
Size: 148 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 “Existence checks”, which interpretation is safe?A command appearing in history proves it completed successfully.A successful first check guarantees that every dependent service is healthy.A successful test usually prints nothing; inspect $? or chain a command.

Apply it elsewhere

Before adapting the test workflow from “Existence checks” 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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