quick and dirty function doc

advanced/learning_bash_scripting.md

@@ -1197,16 +1197,110 @@ done
 
 ## defining a function
 
+```bash
+#!/bin/bash
+
+function say_hello() {
+	echo "hello world"
+}
+
+say_hello
+say_hello
+say_hello
+```
+
 ## function arguments
 
+```bash
+#!/bin/bash
+
+function say_hello() {
+	echo "hello $1"
+}
+
+say_hello
+say_hello "Alice"
+say_hello "Steve" "Camille"
+```
+
 ## global vs local variable
 
+### global example
+
+```bash
+#!/bin/bash
+
+default="my friend"
+
+function say_hello() {
+	if ! [[ -z $1 ]]; then
+		default=$1
+	fi
+	echo "hello $default"
+}
+
+say_hello
+say_hello "Alice"
+say_hello 
+```
+### local example
+
+```bash
+#!/bin/bash
+
+default="my friend"
+
+function say_hello() {
+	if ! [[ -z $1 ]]; then
+		local name=$1
+	else
+		local name=$default
+	fi
+	echo "hello $name"
+}
+
+say_hello
+say_hello "Alice"
+say_hello
+```
+
 ## return values
 
+```bash
+#!/bin/bash
+
+function add_two_numbers() {
+	if [[ -z $1 ]] && [[ -z $2 ]]; then
+		echo "I need two arguments!"
+		return 1
+	elif ! [[ "$1" =~ ^[0-9]+$ ]] || ! [[ "$2" =~ ^[0-9]+$ ]]; then
+		echo "arguments need to be numbers!"
+		return 2
+	fi
+	echo "$1 + $2 = $(( $1 + $2 ))"
+	return 0
+}
+
+add_two_numbers
+echo $?
+add_two_numbers "Alice" "Bob"
+echo $?
+add_two_numbers 3 4
+echo $?
+```
+
 ## the `command` builtin
 
-[Ryan's tutorials](https://ryanstutorials.net/bash-scripting-tutorial/bash-functions.php)
+```bash
+#!/bin/bash
 
+function ls () {
+	echo "I'm a function..."
+}
+
+ls
+command ls /etc/ssh/
+```
 
 # Coding challenge - pipe or argument plus action!