Recursive Functions: Functions That Call Themselves

Recursive functions call themselves. Useful for some problems.

Here's the thing: Recursion is powerful. But use it carefully. It can be slow.

Basic Recursion

function countdown() {
    local n=$1
    if [ $n -le 0 ]; then
        echo "Done"
        return
    fi
    echo "$n"
    countdown $((n - 1))
}

countdown 5

My take: Recursion calls itself. Has a base case. Use it.

Factorial

function factorial() {
    local n=$1
    if [ $n -le 1 ]; then
        echo 1
        return
    fi
    local prev=$(factorial $((n - 1)))
    echo $((n * prev))
}

result=$(factorial 5)
echo "$result"

My take: Factorial is classic recursion. Learn it.

When to Use

Use recursion when:

• Problem is naturally recursive
• Depth is limited
• Code is clearer

Don't use when:

• Depth is unknown
• Performance matters
• Iteration is simpler

My take: Use recursion when it fits. But iteration is often simpler.

Common Mistakes (I've Made These)

1. No base case: Recursion needs base case. Without it, infinite loop.

2. Too deep: Deep recursion can fail. Be careful.

3. Not needed: Sometimes iteration is simpler. Use it.

What's Next?

Now that you understand recursion, let's talk about Function Libraries.

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Personal note: Recursion seemed magical at first. Then I learned it's just functions calling themselves. Now I use it when it fits. But iteration is often simpler.