[OT Personal Memory failure] Can someone remind me how to format code

[reader]

I know there is a keyboard command in emacs that will format a region
of some common kinds of code such as shell script, emacs lisp, perl
etc.

I recall having marked out a region then using some keyboard combo to
format it.

M-x apropos RET format RET   gives far to many confusion hits to find
what I want.