help is a bash command. It uses internal bash structures to store and retrieve information about bash commands.
man is a macro set for the troff (via groff) processor. The output of processing a single file is sent to a pager by the man command by default.
info is a text-only viewer for archives in the info format output of Texinfo.
GNU Info was designed to offer documentation that was comprehensive, hyperlinked, and possible to output to multiple formats.
Man pages were available, and they were great at providing printed output. However, they were designed such that each man page had a reasonably small set of content. A man page might have the discussion on a single C function such as printf(3), or would describe the ls(1) command.
That breaks down when you get into larger systems. How would you fit the documentation for Emacs into man pages? An example of the problem is the Perl man page, which lists 174 separate man pages you can read to get information. How do you browse through that, or do a search to find out what && means?
As an improvement over man pages, Info gave us:
- The ability to have a single document for a large system, which contains all the information about that system. (versus 174 man pages)
- Ability to do full-text search across the entire document (v. man -k which only checks keywords)
- Hyperlinks to different parts of the same or different documents (v. The See Also section, which was made into hyperlinks by some, but not all, man page viewers)
- An index for the document, which could be browsed or you could hit "i" and type in a term and it would search the index and take you to the right place (v. Nothing)
- Linear document browsing across concepts, allowing you read the previous and next sections if you want to, either by mouse or keystroke (v. Nothing).
Is it still relevant? Nowadays most people would say "This documentation doesn't belong in a manpage" and would put it in a PDF or would put it up in HTML. In fact, the help systems on several OSes are based on HTML. However, when GNU Info was created (1986), HTML didn't exist yet. Nowadays texinfo allows you to create PDF, Info, or other formats, so you can use those formats if you want.
That's why GNU Info was invented.
Best Answer
To answer your question with at least a hint of factual background I propose to start by looking at the timeline of creation of
man,infoand other documentation systems.The first
manpage was written in 1971 using troff (nroff was not around yet) in a time when working on a CRT based terminal was not common and printing of manual pages the norm. The man pages use a simple linear structure. The man pages normally give a quick overview of a command, including its commandline option/switches.The
infocommand actually processes the output from Texinfo typesetting syntax. This had its initial release in February 1986, a time when working on a text based CRT was the norm for Unix users, but graphical workstations still exclusive. The.infooutput from Texinfo provides basic navigation of text documents. And from the outset has a different goal of providing complete documentation (for the GNU Project). Things like the use of the command and the commandline switches are only a small part of what an Texinfo file for a program contains.Although there is overlap the (Tex)info system was designed to complement the
manpages, and not to replace them.HTML and web browsers came into existence in the early 90s and relatively quickly replaced text based information systems based on WAIS and gopher. Web browsers utilised the by then available graphical systems, which allows for more information (like underlined text for a hyperlink) then text-only systems allow. As the functionality
infoprovides can be emulated in HTML and a web browser (possible after conversion), the browser based system allow for greater ease of navigation (or at least less experience/learning).HTML was expanded and could do more things than Texinfo can. So for new projects (other than GNU software) a whole range of documentation systems has evolved (and is still evolving), most of them generating HTML pages. A recent trend for these is to make their input (i.e. what the human documenter has to provide) human readable, whereas Texinfo (and troff) is more geared to efficient processing by the programs that transform them.¹
infowas not intended to be a replacement for the man pages, but they might have replaced them if the GNU software had included ainfo2manlike program to generate the man pages from a (subset of a larger) Texinfo file.Combine that with the fact that fully utilising the facilities that a system like Texinfo, (La(TeX, troff, HTML (+CSS) and reStructured Text provide takes time to learn, and that some of those are arguably more easy to learn and/or are more powerful, there is little chance of market dominance of (Tex)
info.¹ E.g reStructured Text, which can also be used to write man pages