Show current <leader> key setting?

To see the current value currently defined for <leader>, use:

:let mapleader

Producing output like:

mapleader ,

It may be undefined if not previously set, defaulting instead to a backslash \

By default mapleader is not set, and special string "<Leader>" means \.

If you do:

:echo mapleader

you will get

Undefined variable: mapleader
Invalid expression: mapleader

If you want to set special string "<Leader>" to a different key, say ",", which is recommended by many, do:

:let mapleader=","

Then

:echo mapleader
,