Bash Scripting Tutorial: Automate Linux Tasks with Shell Scripts

What Are Bash Scripts?

Bash scripts are text files containing a sequence of commands. The shell reads and executes them in order — automating repetitive tasks that would take hours manually. If you run the same three commands every morning, write a bash script instead.

Your First Script

Create a file called hello.sh:

#!/bin/bash
echo "Hello, $(whoami)! Today is $(date +%A)."

Make it executable and run it:

chmod +x hello.sh
./hello.sh

The #!/bin/bash line (shebang) tells the system which interpreter to use.

Variables and Input

#!/bin/bash
NAME="Security Analyst"
read -p "Enter your target: " TARGET
echo "Scanning $TARGET for $NAME work..."

Variables need no type declaration. Use $ to reference them. The read command captures user input.

Conditionals

#!/bin/bash
PORT=22

if [ $PORT -eq 22 ]; then
    echo "SSH is open"
elif [ $PORT -eq 80 ]; then
    echo "HTTP is open"
else
    echo "Unknown service on port $PORT"
fi

Common test operators:

• -eq, -ne, -gt, -lt — numeric comparison
• =, != — string comparison
• -f, -d — file/directory exists
• -z, -n — string empty/not empty

Loops

For Loop:

#!/bin/bash
for ip in 192.168.1.{1..254}; do
    ping -c 1 -W 1 $ip &>/dev/null && echo "$ip is alive"
done

While Loop:

#!/bin/bash
COUNT=1
while [ $COUNT -le 5 ]; do
    echo "Attempt $COUNT"
    ((COUNT++))
done

Functions

#!/bin/bash
check_port() {
    local host=$1
    local port=$2
    timeout 1 bash -c "echo >/dev/tcp/$host/$port" 2>/dev/null
    return $?
}

if check_port 192.168.1.1 22; then
    echo "Port 22 is open"
fi

Functions make scripts modular and reusable. Use local for function variables.

Practical Example: Backup Script

#!/bin/bash
SOURCE="/var/www/html"
DEST="/backups/$(date +%Y%m%d_%H%M%S).tar.gz"
LOG="/var/log/backup.log"

echo "$(date): Starting backup of $SOURCE" >> $LOG
tar -czf "$DEST" "$SOURCE" 2>> $LOG

if [ $? -eq 0 ]; then
    echo "$(date): Backup successful: $DEST" >> $LOG
else
    echo "$(date): Backup FAILED" >> $LOG
fi

Practical Example: Log Analyzer

#!/bin/bash
LOGFILE=$1
echo "=== Failed SSH Attempts ==="
grep "Failed password" "$LOGFILE" | awk '{print $11}' | sort | uniq -c | sort -rn | head -10

Run with: ./analyze.sh /var/log/auth.log

Practical Example: Automated Scanner

#!/bin/bash
TARGET=$1
echo "Scanning $TARGET..."
nmap -sV -oN "scan_$(date +%s).txt" "$TARGET"
echo "Scan complete. Results saved."

Tips for Writing Scripts

1. Always include the shebang line
2. Quote variables to handle spaces: "$VAR"
3. Use set -e to exit on errors
4. Comment non-obvious logic
5. Test with echo before executing real commands
6. Use shellcheck to catch common mistakes

Bash scripting is a force multiplier for Linux administrators and security professionals. Start automating your daily tasks today.