This lesson covers several key topics in Bash scripting: loops, functions, script inputs, and variable scope.

I. Loops in Bash
   - while Loop: Executes one or more instructions while a specified condition is true. It stops when the condition is no longer
                 true or if an explicit interruption like break or continue is used.

   - break Statement: An example is provided showing how to use break to interrupt a while loop immediately when a specific condition is met .

   - until Loop: Executes one or more instructions while a specified condition is false.

   - until vs. while: The key difference is their test condition. The while loop executes as long as its condition is true,
     	       	      whereas the until loop executes as long as its condition is false.


Looping Through Array Elements: Uses the syntax ${myArray[@]} to return all elements in an array. The @ symbol is noted as standing for "all".

Looping Through Array Indices: Uses the syntax ${!myArray[@]} to return all the indices (keys) of an array.

II. Functions in Bash

- Purpose: Functions are used to group sets of logically related commands, which makes those commands reusable without needing to rewrite them.

- Declaration: Unlike in compiled languages, a function does not need to be declared before it is defined.

- Syntax: Functions are defined using the structure function func_name { COMMANDS } .

- Calling: A function is executed (called) simply by writing its name, func_name, in the script .


- Parameters/Arguments: Parameters do not need to be declared. They are read at the beginning of the function using positional parameters ($1, $2, etc.).
                        The syntax for calling a function with parameters is func_name param1 param2 ....

III. Script Utility and Input

- Adding Help: A common practice is to create a function (e.g., display_usage ) that prints usage instructions.
               This function is typically called if the script receives an insufficient number of arguments (checked via [[ $# -le 1 ]]).

- Positional Parameters: These are special variables ($0 through $9) that store the contents of the command line. $0 holds the script's name , while $1, $2, etc.,
                         hold the subsequent parameters. This is the same mechanism used to read parameters inside a function.

IV. Variable Scope

- Scope Types: Variables are generally distinguished as being either Global or Local.

- Block Scope: Bash, much like Python, does not have block scope for variables declared within conditional blocks (like if statements).

- Function Scope: Bash does have local scope within functions.

- local Modifier: This keyword is used to declare a variable as being local to a function.
                  A local variable is visible only from the point it is defined until the function finishes executing.

- Global Variables: By default, a variable defined in the main body of a script is global. It is visible throughout the entire script,
                    including inside any functions . Exported variables are also global and are visible in all subshells.

- Best Practice: The lesson advises to almost never use global variables, as they can lead to wide-ranging and unintended consequences