引言

以neovim的安装过程为例
下载

curl -LO https://github.com/neovim/neovim/releases/latest/download/nvim-linux64.tar.gz
sudo rm -rf /opt/nvim
sudo tar -C /opt -xzf nvim-linux64.tar.gz

添加环境变量前，是无法使用man nvim的
Then add this to your shell config (~/.bashrc, ~/.zshrc, …):

export PATH="$PATH:/opt/nvim-linux64/bin"

通过man man命令，得知man的配置文件为/etc/manpath.config

通过查看可以发现一段

#		*PATH*        ->	*MANPATH*
#
MANPATH_MAP	/bin			/usr/share/man
MANPATH_MAP	/usr/bin		/usr/share/man
MANPATH_MAP	/sbin			/usr/share/man
MANPATH_MAP	/usr/sbin		/usr/share/man
MANPATH_MAP	/usr/local/bin		/usr/local/man
MANPATH_MAP	/usr/local/bin		/usr/local/share/man
MANPATH_MAP	/usr/local/sbin		/usr/local/man
MANPATH_MAP	/usr/local/sbin		/usr/local/share/man
MANPATH_MAP	/usr/X11R6/bin		/usr/X11R6/man
MANPATH_MAP	/usr/bin/X11		/usr/X11R6/man
MANPATH_MAP	/usr/games		/usr/share/man
MANPATH_MAP	/opt/bin		/opt/man
MANPATH_MAP	/opt/sbin		/opt/man

可问题是/opt/下是没有直接的bin目录的，所以可以推测出该配置使得man命令识别了添加了的环境变量/opt/xxx/bin下的/opt/xxx/man下的man文件