Can Bash array indices be negative?

That's a very insightful question about Bash array behavior!

In standard Bash, array indices cannot be negative. They must be non-negative integers (0 or greater).

If you try to access an array element with a negative index, Bash will treat it as an invalid index and typically return an empty string, similar to accessing an out-of-bounds positive index, and it won't produce an error message.

Let's quickly test this:

#!/bin/bash

# Define an array
my_array=("apple" "banana" "cherry")

# Access with a positive index (valid)
echo "Positive index 0: ${my_array[0]}"

# Try to access with a negative index
echo "Negative index -1: ${my_array[-1]}"
echo "Negative index -2: ${my_array[-2]}"

Output:

Positive index 0: apple
Negative index -1:
Negative index -2:

As you can see, using negative indices just results in an empty output.

A Note on other languages:

It's worth noting that some other programming languages (like Python, for example) do allow negative indexing, where -1 refers to the last element, -2 to the second to last, and so on. However, this is not a feature of standard Bash array indexing.

So, when working with Bash arrays, always remember to use 0 and positive integers for your indices!