Shell Scripting

Shell Scripting

Bash Scripting Fundamentals

Script Structure

#!/bin/bash
# Script description
# Author: Your Name
# Date: YYYY-MM-DD

# Variables
NAME="Linux Admin"

# Main script content
echo "Hello, $NAME!"

Variables and Data Types

• String variables
• Numeric variables
• Arrays
• Environment variables

Basic Operations

# String operations
STR="Hello World"
echo ${#STR}          # String length
echo ${STR:0:5}       # String slice

# Arithmetic operations
A=5
B=3
echo $((A + B))       # Addition
echo $((A * B))       # Multiplication

Control Structures

Conditional Statements

if [ $A -eq $B ]; then
    echo "Equal"
elif [ $A -gt $B ]; then
    echo "Greater"
else
    echo "Lesser"
fi

# Case statement
case $VAR in
    1) echo "One" ;;
    2) echo "Two" ;;
    *) echo "Other" ;;
esac

Loops

# For loop
for i in {1..5}; do
    echo $i
done

# While loop
while [ $count -lt 5 ]; do
    echo $count
    ((count++))
done

Script Automation

Functions

# Function definition
greet() {
    local name=$1
    echo "Hello, $name!"
}

# Function call
greet "John"

Command Line Arguments

echo "Script name: $0"
echo "First argument: $1"
echo "All arguments: $@"
echo "Number of arguments: $#"

Input/Output

# Read user input
read -p "Enter name: " name

# File operations
while IFS= read -r line; do
    echo "$line"
done < input.txt

Error Handling and Debugging

Error Handling

# Exit on error
set -e

# Error handling function
handle_error() {
    echo "Error on line $1"
    exit 1
}

trap 'handle_error $LINENO' ERR

Debugging Techniques

# Enable debug mode
set -x

# Debug specific section
set -x
# debugging starts
commands here
set +x
# debugging ends

Hands-on Practice

Exercise 1: Basic Script

1. Create a backup script: ```bash #!/bin/bash

BACKUP_DIR=”/backup” SOURCE_DIR=”/data”

Create backup

tar -czf “$BACKUP_DIR/backup-$(date +%F).tar.gz” “$SOURCE_DIR”

### Exercise 2: System Monitoring
1. Create a system monitoring script:
```bash
#!/bin/bash

while true; do
    echo "Memory Usage:"
    free -h
    echo "CPU Load:"
    uptime
    sleep 5
done

Best Practices

Script Organization

• Use meaningful variable names
• Comment your code
• Modular design
• Version control

Security Considerations

• Input validation
• Secure file permissions
• Avoid shell injection
• Use restricted paths

Additional Resources

• Bash Guide
• Shell Scripting Tutorial
• Advanced Bash Scripting Guide

Next Steps

• Learn advanced scripting techniques
• Study regular expressions
• Explore script testing
• Implement automation solutions