Bash Learning & Automation

Simple notes, commands, and practical examples for learning Bash as part of a DevOps journey.

Why Bash?

Bash is a command-line shell used on Linux and macOS. In DevOps, it helps automate repetitive work such as backups, deployments, log checks, and server maintenance.

Quick Start

Create a file called hello.sh:

#!/usr/bin/env bash

echo "Hello, DevOps!"

Make it executable and run it:

chmod +x hello.sh
./hello.sh

Basic Commands

Command	What it does
pwd	Shows the current folder.
ls -la	Lists files, including hidden files.
cd folder-name	Moves into a folder.
mkdir project	Creates a folder.
touch file.txt	Creates an empty file.
cp source target	Copies a file.
mv old new	Moves or renames a file.
rm file.txt	Deletes a file. Use carefully.
cat file.txt	Prints a file's contents.
grep "text" file.txt	Finds text in a file.

Variables and Input

#!/usr/bin/env bash

NAME="Ada"
echo "Hello, $NAME"

echo "Enter your environment:"
read -r ENVIRONMENT
echo "Deploying to $ENVIRONMENT"

Use arguments when running a script:

#!/usr/bin/env bash

echo "Application: $1"
echo "Environment: $2"

./deploy.sh my-app staging

Conditions and Loops

Check whether a file exists:

if [ -f "config.yml" ]; then
  echo "Configuration found"
else
  echo "Configuration missing"
fi

Loop through files:

for file in *.log; do
  echo "Checking $file"
done

Functions

Functions keep scripts organised and reusable.

say_hello() {
  echo "Hello, $1!"
}

say_hello "DevOps learner"

Useful DevOps Examples

Check disk space

#!/usr/bin/env bash

df -h

Create a dated backup

#!/usr/bin/env bash

SOURCE="./app-data"
BACKUP="backup-$(date +%F).tar.gz"

tar -czf "$BACKUP" "$SOURCE"
echo "Created $BACKUP"

Check whether a service is running

#!/usr/bin/env bash

SERVICE="nginx"

if systemctl is-active --quiet "$SERVICE"; then
  echo "$SERVICE is running"
else
  echo "$SERVICE is not running"
fi

Tips and Best Practices

• Start scripts with #!/usr/bin/env bash.
• Add set -euo pipefail near the top of important scripts to stop on common errors.
• Always quote variables: use "$FILE", not $FILE.
• Use clear variable names such as BACKUP_DIR and LOG_FILE.
• Add comments to explain why a command is needed.
• Test scripts in a safe environment before using them on production servers.
• Never put passwords, API keys, or tokens directly in a script or Git repository.
• Use shellcheck script.sh to find common Bash mistakes.

Handy Cheatsheet

# File permissions
chmod +x script.sh       # make executable
chmod 644 file.txt       # read/write owner; read everyone else

# Redirect output
command > output.txt     # save output (overwrite)
command >> output.txt    # save output (append)
command 2> errors.txt    # save errors

# Pipes
ps aux | grep nginx      # find a process
cat app.log | tail -n 20 # show last 20 lines

# Archive files
tar -czf archive.tar.gz folder/
tar -xzf archive.tar.gz

DevOps Connection

Bash is commonly used to automate server setup, deployment tasks, CI/CD jobs, backups, monitoring checks, and log analysis.

Learning by building: each script in this repository is a small step toward reliable automation.