Shell scripting · Lesson 1 of 31 · 8 minutes

Script shebang review

Read a script header and metadata before execution.

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learner@clairos:~ $

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Your objectives

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1
Read shebang
Run head -n 2 scripts/deploy.sh.
Hint & worked example
Show the beginning of an input; -n sets how many lines to include.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
head -n 2 scripts/deploy.sh
```
Remember: A small sample may omit the failure. Choose the time window you actually need.
2
Inspect script
Run stat scripts/deploy.sh.
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 scripts/deploy.sh
```
Remember: Metadata and file contents answer different questions.
3
Hash script
Run sha256sum scripts/deploy.sh.
Hint & worked example
Compare content digests to detect byte changes, not to establish who authored the file.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
sha256sum scripts/deploy.sh
```
Remember: A checksum detects changes only relative to a trusted expected digest.

Understand the pattern

Junior operators build confidence by gathering evidence before changing systems.

head: Show the beginning of an input; -n sets how many lines to include.
A small sample may omit the failure. Choose the time window you actually need.
stat: Inspect a file or directory metadata record, including ownership, permissions, and size.
Metadata and file contents answer different questions.
sha256sum: Compare content digests to detect byte changes, not to establish who authored the file.
A checksum detects changes only relative to a trusted expected digest.

Worked example and expected result

$ head -n 2 scripts/deploy.sh

#!/bin/sh
set -eu

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

$ stat scripts/deploy.sh

Path: /home/learner/scripts/deploy.sh
Type: file
Mode: -rw-r--r--
Owner: learner
Group: learners
Size: 85 bytes

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

$ sha256sum scripts/deploy.sh

f7d569c8d8504a5ddbe9ac442362c65f068aeacd1f540b24ca1ec84b7c27359e  /home/learner/scripts/deploy.sh

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 shebang 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.Metadata and file contents answer different questions.

Apply it elsewhere

Before adapting the stat workflow from “Script shebang 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.

Next: Script-style output Try an incident drill

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