Regex (php) to extract only numbers or only letters inside square brackets (excluding the brackets)

Question

I have this regex that extracts anything inside braquets: [^[\]]+(?=])

1) I want to extract the content within the brackets as a whole if it contains letters only (a-z)

2) I want to extract the content within the brackets as a whole if it contains numbers only (0-9)

So, I need 2 regex.

Answer 1

Try this

(?<=\[)[a-zA-Z]+(?=\])

Demo

(?<=\[)[0-9]+(?=\])

Demo