CLI scripting basics in AWS - Commands & Configuration

Introduction

Using the AWS CLI lets you control cloud services from your computer by typing commands. Scripting these commands helps automate tasks, saving time and avoiding mistakes.

When you want to create or delete cloud resources without clicking in the web console.

When you need to repeat the same setup steps for multiple projects quickly.

When you want to schedule tasks like backups or updates to run automatically.

When you want to check the status of your cloud resources from your terminal.

When you want to combine multiple AWS commands into one script for efficiency.

Commands

This command sets your default AWS region to us-east-1 so that all commands run in this location unless specified otherwise.

Terminal

aws configure set region us-east-1

Expected Output

No output (command runs silently)

This command creates a new S3 bucket named example-bucket-cli-scripting to store files in the cloud.

Terminal

aws s3 mb s3://example-bucket-cli-scripting

Expected Output

make_bucket: example-bucket-cli-scripting

This command lists all your S3 buckets so you can verify the new bucket was created.

Terminal

aws s3 ls

Expected Output

2024-06-01 12:00:00 example-bucket-cli-scripting

This command deletes the S3 bucket example-bucket-cli-scripting and all its contents. The --force flag is needed to remove non-empty buckets.

Terminal

aws s3 rb s3://example-bucket-cli-scripting --force

Expected Output

remove_bucket: example-bucket-cli-scripting

→

--force - Deletes all objects in the bucket before removing the bucket itself.

Key Concept

If you remember nothing else, remember: AWS CLI commands can be combined in scripts to automate cloud tasks safely and quickly.

Common Mistakes

Not setting the AWS region before running commands.

Commands may fail or run in the wrong region, causing confusion or errors.

Always run 'aws configure set region your-region' before other commands.

Trying to delete a non-empty S3 bucket without the --force flag.

AWS will refuse to delete buckets that still have files inside.

Use the --force flag to delete all contents before removing the bucket.

Typing commands with incorrect bucket names or typos.

Commands will fail because the resource does not exist or is misspelled.

Double-check names and use copy-paste to avoid typos.

Summary

Set your AWS region first to ensure commands run in the right place.

Create and list S3 buckets using simple AWS CLI commands.

Use the --force flag to delete buckets that contain files.

Practice

1. What does the AWS CLI command aws s3 ls do?

easy

A. Deletes all S3 buckets in your AWS account

B. Creates a new S3 bucket

C. Lists all S3 buckets in your AWS account

D. Uploads a file to an S3 bucket

Solution

1. Step 1: Understand the command structure

   The command uses aws s3 which relates to the S3 service, and ls which means list.

2. Step 2: Interpret the command action

   Listing in S3 context means showing all buckets or objects. Without extra parameters, it lists all buckets.

3. Final Answer:

   Lists all S3 buckets in your AWS account -> Option C

4. Quick Check:

   Command aws s3 ls lists buckets [OK]

Hint: Remember: 'ls' means list, so it shows existing resources [OK]

Common Mistakes:

• Confusing 'ls' with 'rm' (delete)
• Thinking it creates resources
• Assuming it uploads files

2. Which of the following is the correct syntax to create an EC2 instance using AWS CLI?

easy

A. aws ec2 run-instances --image-id ami-12345678 --count 1

B. aws ec2 create-instance --image-id ami-12345678 --count 1

C. aws ec2 start-instance --image-id ami-12345678 --count 1

D. aws ec2 launch-instance --image-id ami-12345678 --count 1

Solution

1. Step 1: Identify the correct AWS CLI command for EC2 instance creation

   The official command to create EC2 instances is run-instances.

2. Step 2: Check the syntax correctness

   aws ec2 run-instances --image-id ami-12345678 --count 1 uses aws ec2 run-instances --image-id ami-12345678 --count 1, which is the correct syntax to launch one instance.

3. Final Answer:

   aws ec2 run-instances --image-id ami-12345678 --count 1 -> Option A

4. Quick Check:

   EC2 instance creation uses 'run-instances' command [OK]

Hint: Use 'run-instances' to launch EC2, not 'create-instance' [OK]

Common Mistakes:

• Using 'create-instance' which is invalid
• Confusing 'start-instance' with creation
• Using 'launch-instance' which is not a valid command

3. What will be the output of this AWS CLI command?

aws s3api list-buckets --query 'Buckets[].Name' --output json

medium

A. A JSON array of bucket names

B. A list of bucket creation dates

C. An error because of wrong syntax

D. A plain text list of bucket names

Solution

1. Step 1: Understand the command components

   The command uses list-buckets to get all buckets, with a query to extract only the bucket names.

2. Step 2: Analyze the output format

   The --output json option formats the result as JSON, so the output is a JSON array of bucket names.

3. Final Answer:

   A JSON array of bucket names -> Option A

4. Quick Check:

   Query filters names, output json formats as JSON array [OK]

Hint: Query filters data, output json formats it as JSON [OK]

Common Mistakes:

• Expecting plain text instead of JSON
• Confusing bucket names with creation dates
• Assuming syntax error due to query

4. You run this command to delete an S3 bucket:

aws s3 rb s3://my-bucket

But it fails with an error. What is the most likely cause?

medium

A. You need to use aws s3 rm instead

B. The bucket is not empty

C. The bucket name is invalid

D. The AWS CLI is not installed

Solution

1. Step 1: Understand the command purpose

   aws s3 rb removes (deletes) an S3 bucket, but only if it is empty.

2. Step 2: Identify the common error cause

   If the bucket contains files, the command fails. You must delete all objects first.

3. Final Answer:

   The bucket is not empty -> Option B

4. Quick Check:

   Bucket must be empty before removal [OK]

Hint: Empty bucket before deleting with 'rb' command [OK]

Common Mistakes:

• Trying to delete non-empty bucket directly
• Confusing 'rm' (remove objects) with 'rb' (remove bucket)
• Assuming AWS CLI is not installed without checking

5. You want to write a script that lists all EC2 instances and then stops each one. Which AWS CLI commands should you combine in the script?

hard

A. Use aws ec2 show-instances to list, then aws ec2 power-off-instances to stop

B. Use aws ec2 list-instances to list, then aws ec2 terminate-instances to stop

C. Use aws ec2 get-instances to list, then aws ec2 shutdown-instances to stop

D. Use aws ec2 describe-instances to list, then aws ec2 stop-instances --instance-ids to stop

Solution

1. Step 1: Identify the correct command to list EC2 instances

   The correct command to list instances is describe-instances.

2. Step 2: Identify the correct command to stop instances

   To stop instances, use stop-instances with the instance IDs.

3. Step 3: Combine commands in script logic

   First list instances to get IDs, then stop them using those IDs.

4. Final Answer:

   Use aws ec2 describe-instances to list, then aws ec2 stop-instances --instance-ids to stop -> Option D

5. Quick Check:

   List with describe, stop with stop-instances [OK]

Hint: List with 'describe-instances', stop with 'stop-instances' [OK]

Common Mistakes:

• Using non-existent commands like 'list-instances'
• Confusing 'terminate' with 'stop' (termination deletes)
• Using wrong commands that cause errors