Write a complex script that simulates a basic login system. The script should:

→ Take a username and password as input.

→ Use arrays to store valid usernames and their corresponding passwords.

→ Use a `case` statement to check if the username exists.

→ If the username exists, use an `if` statement to check if the password matches.

→ Print a success message if both username and password are correct, otherwise print an error message.

Write a script that uses an array to store a list of valid usernames. Take a username as input and use a `case` statement to check if the input username is in the list. Print an appropriate message.

Write a script that takes a user input for a day and time (morning, afternoon, evening) and prints a specific message for each combination using nested `case` statements.

Write a script that takes a command-line argument and prints whether it is a start, stop, or restart command using a `case` statement. If the argument is none of these, print a usage message.

Write a script that takes a filename as input and checks if the file is a text file (*.txt), image file (*.jpg, *.png), or an unknown type using a `case` statement with wildcards.

Write a script that takes a day of the week as input and prints whether it is a weekday or weekend using a `case` statement.

Write a script that takes a string as input and checks if the string starts with "A" and ends with "Z". Use `[[ ]]` for the condition.

Write a script that checks if a given file exists and whether it is readable and writable.

Write a script that takes a username and age as input. Check if the username is not empty and the age is greater than 18. Print an appropriate message.

Write a script that takes two numbers as input and checks if the first number is greater than, less than, or equal to the second number.

Write a script that compares two strings input by the user and prints if they are equal or not.

Write a script that attempts to create a directory. Check the exit code of the `mkdir` command and print whether the directory was created successfully or not.

Write a script that takes two numbers as input and checks if both numbers are positive using logical AND. Print an appropriate message.

Write a script that takes a user's age as input and prints whether the user is a child, teenager, adult, or senior citizen.

Write a script that checks if a given number is positive, negative, or zero, and prints an appropriate message.

Write a script that takes a user input number and prints whether the number is positive or non-positive.

Write a script that checks if a given number is positive and prints "The number is positive."

What is a `case` statement in Bash scripting? How does it differ from multiple `if-elif` statements?

What is the `test` directive in Bash, and how is it used within `if` conditions? Explain with an example.

What is an exit code in Bash scripting? How can you check the exit code of the last executed command?

Describe the purpose of `elif` in Bash scripting and how it differs from `if` and `else`.

Explain the basic syntax of an `if` statement in Bash scripting and provide an example.