Under Unix, different documentations are available to learn how to use a command, its options, and its possible arguments.

man: the manual pages

The man command allows access to the documentation of a command on the terminal. man is followed by the name of the command for which you want documentation.

man ls
man man
  • man -k allows you to search for a keyword in man pages.

info: hypertext documentation

The command info provides access to documentation that is often more complete than man. In contrast to man which describes a command in a single page (which can be very long), info uses hypertext to allow a navigation in the documentation.

A summary of the commands under info is obtained by typing ? When executing 'info'.

info info
info ls

/usr/share/doc: the official software documentation

When a software is installed from its source code, all documentation is usually placed in /usr/share/doc. This documentation can be very varied (.txt, .ps, .pdf, etc.) and does not necessarily concern only the use of the command.