man page
A manual end user may invoke a documentation page by issuing the man command followed by the specific detail they require.
These manual pages are typically requested by end users, programmers and administrators doing real time work but can also be formatted for printing.
The environment variable MANPATH often specifies a list of directory paths to search for the various documentation pages.
Before Unix (e.g., GCOS), documentation was printed pages, available on the premises to users (staff, students...), organized into steel binders, locked together in one monolithic steel reading rack, bolted to a table or counter, with pages organized for modular information updates, replacement, errata, and addenda.
The first actual man pages were written by Dennis Ritchie and Ken Thompson at the insistence[citation needed] of their manager Doug McIlroy in 1971.
Aside from the man pages, the Programmer's Manual also accumulated a set of short papers, some of them tutorials (e.g. for general Unix usage, the C programming language, and tools such as Yacc), and others more detailed descriptions of operating system features.
At the time, the availability of online documentation through the manual page system was regarded as a great advance.
The modern descendants of 4.4BSD also distribute man pages as one of the primary forms of system documentation (having replaced the old -man macros with the newer -mdoc).
This makes it possible to typeset a man page into PostScript, PDF, and various other formats for viewing or printing.
Some Unix systems have a package for the man2html command, which enables users to browse their man pages using an HTML browser.
Most systems today (e.g. BSD,[15] macOS, Linux,[16] and Solaris 11.4) inherit the numbering scheme used by Research Unix.
All man pages follow a common layout that is optimized for presentation on a simple ASCII text display, possibly without any form of highlighting or font control.
[22] The man macro set provides minimal rich text functions, with directives for the title line, section headers, (bold, small or italic) fonts, paragraphs and adding/reducing indentation.
The BSD mandoc however only supports bold and underlined (as a replacement for italics) text via the typewriter backspace-then-overstrike sequence, which needs to be translated into ECMA-48 by less.
Examples include GNU's help2man, which takes a --help output and some additional content to generate a manual page.
All these tools emit the man format, as Markdown is not expressive enough to match the semantic content of mdoc.
