In scripts we have the ability to define and call functions. As in any programming language, functions in bash are chunks of code, but there are other differences.

In bash, functions are a sequence of commands grouped under a single name, that is the _name_ of the function. Calling a function is the same as calling any other program, you just write the name and the function will be _invoked_.

We can declare our own function this way:

```bash
my_func () {
  # statements
}

my_func # call my_func
```

We must declare functions before we can invoke them.

Functions can take on arguments and return a result — exit code. Arguments, within functions, are treated in the same manner as arguments given to the script in [non-interactive](#non-interactive-mode) mode — using [positional parameters](#positional-parameters). A result code can be _returned_ using the `return` command.

Below is a function that takes a name and returns `0`, indicating successful execution.

```bash
# function with params
greeting () {
  if [[ -n $1 ]]; then
    echo "Hello, $1!"
  else
    echo "Hello, unknown!"
  fi
  return 0
}

greeting World  # Hello, World!
greeting        # Hello, unknown!
```

The `return` command without any arguments returns the exit code of the last executed command. Above, `return 0` will return a successful exit code `0`.

We can also declare a variable local to a single function using the `local` keyword. Doing so causes the variable to disappear when the function exits.

```bash
local local_var="I'm a local value"
```

## THE CHALLENGE

Create a file named `functions.bash`.

The problem is almost the same as in the previous exercise. You receive two positional parameters and should output all even numbers in the range between them. To do this, create a function with any name that will print these numbers using recursion. Also declare a function `main` that will print the value of `$FUNCNAME` and call your function.

In other words, you should build a tree of even numbers. On the top of the tree should be the name of the `main` function. Other elements must be even numbers. Each new element of the tree should have indentation that is equal to depth (one level is one space ` `).

Example:

    ./loops.bash 10 17

Output:

    main
     10
      12
       14
        16

Use `-n` with `echo` to output something on the same line.

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