Variable Scope: Where Variables Work

Variables have scope. Global. Local. Understand it.

Here's the thing: Scope matters. Global variables are everywhere. Local variables are in functions.

Global Variables

name="John"

function greet() {
    echo "Hello, $name"
}

greet

My take: Global variables are available everywhere. In functions too.

Local Variables

function example() {
    local count=10
    echo "$count"
}

example
echo "$count"  # Empty - not available

My take: local makes variables local. Use it in functions.

Why It Matters

Without Local

count=0

function increment() {
    count=$((count + 1))
}

increment
echo "$count"  # Changed!

My take: Without local, you change global variables. Be careful.

With Local

count=0

function increment() {
    local count=$((count + 1))
    echo "$count"
}

increment
echo "$count"  # Still 0

My take: With local, you don't change global. Safer.

Common Patterns

Use Local in Functions

function process() {
    local temp_file="/tmp/process_$$"
    # Use temp_file
}

Common Mistakes (I've Made These)

1. Not using local: Use local in functions. Avoid conflicts.

2. Changing globals: Be careful. Don't change globals accidentally.

3. Not understanding scope: Understand where variables are available.

What's Next?

Now that you understand scope, let's talk about Best Practices for variables.

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Personal note: Scope confused me at first. Then I learned: use local in functions. Now I do it always. It prevents problems.