Here is conversation about man and info from IRC, nicknames changed:
Yellow: man searches man pages, and info searches info pages.
on a Debian system, man pages live in /usr/share/man and are in nroff format
info pages live in /usr/share/info and are in texinfo format
Blue: man diff AND info diff show identical result
Yellow: then you don’t have the diff info page installed, if you don’t have one or the other installed, you’re probably getting the one in the other’s reader…
does «info diff» say «File: manpages» at the top?
Yellow: then it found no such info page, so it gave you a man page instead, they’re not for the same thing. info shows you info pages, and falls back to manpages
Red: info pages are for pissing you the fuck off.
Yellow: you can’t see info pages via man. though some info pages may have been converted to nroff
Blue: ok, how to choose in what case me need one of this tools ?
Yellow: The GNU people write their documentation primarily in info (texinfo) format, and the man pages are an afterthought, and are generally incomplete.
This pisses off everyone else, because we’re all accustomed to using man pages as THE authoritative source, and the man page interface is SO much easier.
Red: i hate info pages
Yellow: On any non-GNU system, there is no such thing as an info page. There are only man pages, or printed docs.
Blue: Big thanks
Green: oh, I missed the weekly info pages whining