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

Answer 1

It is checking whether the options for the shell $- contains an i in them. The i is for interactive

From the Bash man page:

An interactive shell is one started without non-option arguments and without the -c option whose standard input and error are both connected to terminals (as determined by isatty(3)), or one started with the -i option. PS1 is set and $- includes i if bash is interactive, allowing a shell script or a startup file to test this state.

Also relevant

Answer 2

$- 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.