Monday, April 20, 2026

Cohort 3 | Project CloudIgnite Topics: Bash Scripting (Conditionals, Loops, Control Flow), Linux Software Management, Installing AWS CLI Duration: ~3 hours

☁️ AWS Certified Cloud Practitioner (CLF-C02) relevance is flagged throughout with this symbol.

Key Takeaways

• Bash scripting: #!/bin/bash shebang, if/elif/else/fi, for/while/until loops, break/continue
• Package managers: yum (Amazon Linux/Red Hat), apt (Ubuntu/Debian)
• AWS CLI: Download, unzip, install with ./aws/install, configure with aws configure
• Lab: Backup script using tar -czvf with date-stamped filenames
• exit codes: 0 = success, non-zero = error; $? checks last command's exit code

Table of Contents

1. Bash Scripting Recap
2. Conditional Statements
3. Loops
4. Loop Control — break & continue
5. Other Bash Concepts
6. Lab — Backup Script
7. Linux Software Management
8. Lab — Installing AWS CLI
9. Quiz Review
10. CLF-C02 Relevance Summary

1. Bash Scripting Recap

Basic structure

#!/bin/bash          # Shebang — always the first line; tells the OS which shell to use

echo "Enter your name:"
read name            # Reads input from terminal into variable 'name'
echo "Hello $name"

• echo — prints output to terminal
• read — reads user input into a variable
• Variables — no spaces around =; reference with $varname
• Shebang (#!/bin/bash) — specifies the interpreter; without it, the default shell is used (may vary)

Running a script

chmod +x script.sh   # Give execute permission (or use chmod 744)
./script.sh          # Run using relative path (dot-slash)

Why ./? Without it, the shell looks for the script inside directories listed in the $PATH variable, not the current directory.

2. Conditional Statements

Basic if-else syntax

if [ condition ]; then
    # do something
else
    # do something else
fi                   # 'fi' closes the if block (reverse of 'if')

if-elif-else (multiple conditions)

if [ $1 -gt $2 ]; then
    echo "First number is greater"
elif [ $1 -lt $2 ]; then
    echo "Second number is greater"
else
    echo "Numbers are equal"
fi

Checking if a file exists

read -p "Enter file name to delete: " filename
if [ -f "$filename" ]; then
    echo "Deleting file..."
    rm "$filename"
else
    echo "File does not exist."
fi

Common comparison operators

Tip: The symbol equivalents (>, <, ==) are easier to remember (same as Python/Java/C++). Both styles work in bash.

File test operators

Exit codes

• $? — holds the exit code of the last command
• 0 = success; non-zero = failure/error
• Useful for checking if a command ran successfully:

cp file1 /tmp
if [ $? -eq 0 ]; then
    echo "Copy successful"
fi

Brackets quick reference

3. Loops

For loop

# Explicit list
for file_name in file1 file2 file3 file4; do
    touch "$file_name"
done

# Using a range (brace expansion)
for i in {1..10}; do
    touch "file$i"
done

While loop

counter=1
while [ $counter -le 5 ]; do
    echo "Current value: $counter"
    ((counter++))        # Increment counter
done
echo "Loop exited"

• Executes as long as the condition is true
• Always increment your counter — forgetting this creates an infinite loop

Until loop

until [ condition ]; do
    # runs until condition becomes TRUE
done

• Opposite of while — runs while condition is false
• You can do everything with for/while; until is optional to know

while true — infinite loop (use with caution!)

while true; do
    read -p "Guess the number: " guess
    if [ $guess -eq 7 ]; then
        break       # Only way out
    fi
done

⚠️ An infinite loop without a break will spike CPU usage. Always have an exit condition. Press Ctrl+C to kill a runaway loop.

4. Loop Control — break & continue

break

Exits the loop immediately when a condition is met.

for i in {1..50}; do
    if [ $i -eq 10 ]; then
        break        # Stops at 10, even though loop goes to 50
    fi
    echo $i
done

continue

Skips the remaining statements in the current iteration and moves to the next one.

for i in {1..15}; do
    if [ $i -eq 10 ]; then
        continue     # Skips printing 10
    fi
    echo $i
done
# Output: 1 2 3 4 5 6 7 8 9 11 12 13 14 15

Practical note: break is used frequently; continue is rarer but useful for skipping specific values.

5. Other Bash Concepts

Exit command

exit 0    # Successful execution
exit 1    # Error occurred (any non-zero = problem)

Command substitution

Embed the output of a command directly into a variable or string:

current_date=$(date +%Y_%m_%d)
echo "Today is $current_date"

printf

Similar to printf in C/Python — formatted output.

Running scripts — path rules

To make a script runnable from anywhere, add its directory to $PATH.

Vim — show line numbers

:set number      # Inside vim, in command mode

Or add set number to ~/.vimrc for it to be permanent.

6. Lab — Backup Script

Task: Write a bash script that creates a compressed backup of a folder named company_a. The archive filename must include today's date in YYYY_MM_DD format.

Solution walkthrough

#!/bin/bash

# Step 1: Get today's date
day=$(date +%Y_%m_%d)

# Step 2: Define the backup file path
backup_name="/home/ec2-user/backups/${day}_backup_company_a.tar.gz"

# Step 3: Create the compressed archive
tar -czvf "$backup_name" /home/ec2-user/company_a

echo "Backup created: $backup_name"

Key tar flags

Setup steps

touch backup.sh
chmod +x backup.sh    # or: chmod 744 backup.sh
vim backup.sh         # Write the script
./backup.sh           # Run it

Common mistake: Using $name as the rm target without specifying the path. Use rm $(pwd)/$name or provide the full path.

7. Linux Software Management

Package managers by distribution

Amazon Linux EC2 instances are based on Red Hat, so use yum or dnf.

Common yum commands

sudo yum check-update              # Check for available updates
sudo yum update --security         # Apply security updates only
sudo yum upgrade                   # Upgrade all packages
sudo yum install -y httpd          # Install Apache web server (-y = yes to all prompts)
sudo yum history                   # View install history
sudo yum history info <ID>         # Details of a specific install action
sudo yum history undo <ID> -y      # Roll back / undo an installation

Two ways to install software on Linux

1. Package manager — downloads pre-compiled binary from a repository. Easiest and most common.
2. Source code — download source (e.g., git clone), compile manually, then install. Slower but gives full control.

Repositories

• A repository is a server that stores packaged (pre-compiled) software.
• Amazon Linux has two main repos: Amazon 2 Core (OS packages) and Amazon 2 Extra (Docker etc.)
• Package manager fetches software from the repo automatically.

Downloading files from terminal (no browser on EC2!)

wget http://example.com/software.zip          # Simple download
curl -o software.zip http://example.com/software.zip   # More flexible

wget can auto-resume interrupted downloads; curl requires manual flags to do the same.

8. Lab — Installing AWS CLI

Objective: Download, install, and configure the AWS CLI on a Red Hat-based EC2 instance.

Steps

# 1. Check Python is available (AWS CLI v2 requires it)
python3 --version
pip3 --version

# 2. Download AWS CLI zip using curl
curl "https://awscli.amazonaws.com/awscli-exe-linux-x86_64.zip" -o "awscliv2.zip"

# 3. Unzip
unzip awscliv2.zip

# 4. Install
sudo ./aws/install

# 5. Verify
aws --version
aws help          # Press Q to quit

Configure AWS CLI

aws configure
# AWS Access Key ID:     [press Enter — or paste key]
# AWS Secret Access Key: [press Enter — or paste key]
# Default region name:   us-west-2
# Default output format: json

Where to find credentials (in AWS lab environment)

• In the lab panel → Details → Show → copy [default] block including both = signs at the end of the secret key

Save credentials manually

sudo nano ~/.aws/credentials
# Paste the [default] block
# Ctrl+O → Enter (save) → Ctrl+X (exit)

Verify installation

aws ec2 describe-instances \
  --instance-ids <your-instance-id> \
  --query "Reservations[].Instances[].InstanceType"

If it returns an instance type (e.g., t3.micro), the CLI is working correctly.

☁️ CLF-C02 relevance: AWS CLI is a core tool for interacting with AWS services programmatically — understanding it supports the "Cloud Technology and Services" domain.

9. Quiz Review

10. CLF-C02 Relevance Summary

The CLF-C02 exam focuses on AWS services and cloud concepts, not deep Linux/bash knowledge. However, the following from today's lecture is relevant:

💡 Study tip (from the instructor): For the CLF-C02, focus your energy on knowing AWS services — what each service does, when to use it, and roughly how it's priced. Linux and Python questions will be minimal on that exam.

Key Takeaways

• Bash scripting is a core DevOps skill — you don't need to memorize all syntax; understand the concepts and look up syntax when needed.
• Conditionals (if/elif/else/fi), loops (for/while), and exit codes (0 = success) are the essential building blocks.
• Use ./script.sh to run scripts in the current directory; add to $PATH to run from anywhere.
• On Red Hat/Amazon Linux, use yum for package management; apt is for Debian/Ubuntu.
• AWS CLI is installed via curl + unzip + ./aws/install and configured with aws configure.
• Always specify the correct AWS region when configuring the CLI — it must match where your resources are running.

Notes compiled from lecture — April 20, 2026 · Cohort 3: Project CloudIgnite