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Practice Exercise: Advanced Bash Shell Scripting Techniques

Objectives

  • Explore advanced Bash shell scripting techniques.
  • Learn how to use arrays, functions, and advanced scripting concepts.
  • Practice creating complex Bash scripts to solve real-world problems.

Scenario

In this exercise, you will dive deeper into advanced Bash shell scripting techniques. You will explore topics like arrays, functions, command-line arguments, and error handling. These techniques are valuable for creating robust and efficient Bash scripts.

Tasks

Task 1: Working with Arrays

  • Create a Bash script named array_operations.sh.
  • Define an array that stores the names of your favorite fruits.
  • Write a loop to iterate through the array and display each fruit's name.
  • Implement an array operation to add a new fruit to the list.
  • Modify the script to remove a specific fruit from the array.
  • Test the array operations and ensure they work correctly. 
    #!/bin/bash

# Define an array of favorite fruits
fruits=("Apple" "Banana" "Cherry" "Grape" "Orange")

# Function to display all fruits in the array
display_fruits() {
    echo "My favorite fruits are:"
    for fruit in "${fruits[@]}"; do
        echo "- $fruit"
    done
}

# Function to add a new fruit to the array
add_fruit() {
    local new_fruit="$1"
    fruits+=("$new_fruit")
    echo "$new_fruit has been added to the list of favorite fruits."
}

# Function to remove a specific fruit from the array
remove_fruit() {
    local fruit_to_remove="$1"
    for index in "${!fruits[@]}"; do
        if [ "${fruits[$index]}" == "$fruit_to_remove" ]; then
            unset fruits[$index]
            echo "$fruit_to_remove has been removed from the list of favorite fruits."
            return
        fi
    done
    echo "$fruit_to_remove was not found in the list of favorite fruits."
}

# Display the initial list of fruits
display_fruits

# Add a new fruit to the list
add_fruit "Mango"

# Display the updated list of fruits
display_fruits

# Remove a specific fruit from the list
remove_fruit "Cherry"

# Display the final list of fruits
display_fruits

    [intern@intern-a1t-inf-lnx1 ~]$ chmod +x array_operations.sh
[intern@intern-a1t-inf-lnx1 ~]$ ./array_operations.sh
My favorite fruits are:
- Apple
- Banana
- Cherry
- Grape
- Orange
Mango has been added to the list of favorite fruits.
My favorite fruits are:
- Apple
- Banana
- Cherry
- Grape
- Orange
- Mango
Cherry has been removed from the list of favorite fruits.
My favorite fruits are:
- Apple
- Banana
- Grape
- Orange
- Mango

Task 2: Implementing Functions

  • Create a Bash script named math_functions.sh.
  • Write a Bash function that calculates the square of a given number.
  • Implement another function that finds the factorial of a positive integer.
  • Call these functions with different input values and display the results.
  • Document your functions and their usage within the script. 
    #!/bin/bash

# Function to calculate the square of a number
calculate_square() {
    local number=$1
    local square=$((number * number))
    echo "The square of $number is: $square"
}

# Function to calculate the factorial of a positive integer
calculate_factorial() {
    local n=$1
    local factorial=1

    if [ $n -lt 0 ]; then
        echo "Factorial is not defined for negative numbers."
        return
    fi

    for ((i = 1; i <= n; i++)); do
        factorial=$((factorial * i))
    done

    echo "The factorial of $n is: $factorial"
}

# Example usages of the functions
calculate_square 5
calculate_square 7

calculate_factorial 5
calculate_factorial 0
calculate_factorial -3

    [intern@intern-a1t-inf-lnx1 ~]$ chmod +x math_functions.sh
[intern@intern-a1t-inf-lnx1 ~]$ ./math_functions.sh
The square of 5 is: 25
The square of 7 is: 49
The factorial of 5 is: 120
The factorial of 0 is: 1
Factorial is not defined for negative numbers.

Task 3: Command-Line Arguments

  • Create a Bash script named command_line_args.sh.
  • Write a script that accepts command-line arguments.
  • Use positional parameters to capture and display the arguments.
  • Implement error handling to check if the correct number of arguments is provided.
  • Provide a usage message when incorrect usage is detected. 
    #!/bin/bash

# Check the number of command-line arguments
if [ $# -eq 0 ]; then
    echo "Usage: $0 <arg1> <arg2> ..."
    exit 1
fi

# Display the provided command-line arguments
echo "You provided the following arguments:"

# Loop through and display each argument
for arg in "$@"; do
    echo "$arg"
done

[intern@intern-a1t-inf-lnx1 ~]$ chmod +x command_line_args.sh
[intern@intern-a1t-inf-lnx1 ~]$ ./command_line_args.sh
Usage: ./command_line_args.sh <arg1> <arg2> ...
[intern@intern-a1t-inf-lnx1 ~]$ ./command_line_args.sh echo gg
You provided the following arguments:
echo
gg

Task 4: Combining Techniques

  • Create a Bash script named advanced_script.sh.
  • Combine the techniques you've learned in previous tasks to create a comprehensive script.
  • Use arrays to store data, functions to perform calculations, and command-line arguments for customization.
  • Implement error handling to deal with potential issues.
  • Test the script with various inputs to ensure it works as expected. 
    [intern@intern-a1t-inf-lnx1 ~]$ cat advance_script.sh
#!/bin/bash

# Function to calculate the square of a number
calculate_square() {
    local num=$1
    local square=$((num * num))
    echo "The square of $num is $square"
}

# Function to find the factorial of a positive integer
calculate_factorial() {
    local num=$1
    local factorial=1

    if [ $num -lt 0 ]; then
        echo "Error: Factorial is undefined for negative numbers."
        return 1
    fi

    for ((i = 1; i <= num; i++)); do
        factorial=$((factorial * i))
    done

    echo "The factorial of $num is $factorial"
}

# Check the number of command-line arguments
if [ $# -lt 2 ]; then
    echo "Usage: $0 <square|factorial> <value>"
    exit 1
fi

# Parse command-line arguments
operation="$1"
value="$2"

case "$operation" in
    "square")
        calculate_square "$value"
        ;;
    "factorial")
        calculate_factorial "$value"
        ;;
    *)
        echo "Invalid operation. Supported operations: square, factorial."
        exit 1
        ;;
esac

    [intern@intern-a1t-inf-lnx1 ~]$   chmod +x advance_script.sh
[intern@intern-a1t-inf-lnx1 ~]$ ./advance_script.sh
Usage: ./advance_script.sh <square|factorial> <value>
[intern@intern-a1t-inf-lnx1 ~]$ ./advance_script.sh asdf 3
Invalid operation. Supported operations: square, factorial.
[intern@intern-a1t-inf-lnx1 ~]$ ./advance_script.sh factorial -1
Error: Factorial is undefined for negative numbers.
[intern@intern-a1t-inf-lnx1 ~]$ ./advance_script.sh factorial 4
The factorial of 4 is 24
[intern@intern-a1t-inf-lnx1 ~]$ ./advance_script.sh square -2
The square of -2 is 4

Conclusion

In this exercise, you've explored advanced Bash shell scripting techniques, including arrays, functions, command-line arguments, and error handling. These skills are essential for creating complex and reliable Bash scripts to solve real-world problems. Continue to practice and refine your scripting abilities for more advanced tasks.