What does [[ $- = *i* ]] mean in bash?

Question

I'm installing liquidprompt and in the documentation they ask you to add [[ $- = *i* ]] && source ~/liquidprompt/liquidprompt in your .bashrc .

I am trying to understand the first part of the line but it's hard for a noob in bash like me. If anyone has a nice doc or the answer...

Answer 1

$- contains the current shell options.

In [[ ... ]], the right hand side of a = is interpreted as a pattern if not quoted. Therefore, *i* means i possibly preceded or followed by anything.

In other words, it checks wheter the i option is present, i.e. whether the current shell is interactive.