Ubuntu – How to follow a link in man

The references in square brackets on the git man page seem to be referencing footnotes from the same page rather than being references to other man page. From the bottom of the git man page:

NOTES
    1. Everyday Git
       file:///usr/share/doc/git-doc/everyday.html

About UNIX(7)

To answer your question of "UNIX(7)", this is standard convention of saying "The man page for UNIX in section 7 (miscellaneous)".

To open a page like init(8), you would use this command: man 8 init.

man regex vs man 7 regex

To answer your question of the 'subtle differences' between man regex and man 7 regex:

man by default opens the page with the lowest section number. In this case, it is section 3 (Library calls). Opening the page from section 7 (Miscellaneous) is quite different.

Pages in different sections address different things, though in this case they are similar, consider apt:

man -f apt:

apt (8)              - Advanced Package Tool
apt (1)              - annotation processing tool

In this example, apt from section 8 (System administration commands) is completely unrelated to the page from section 1 (Executable programs or shell commands).

For future reference, use man -f PAGE_NAME to locate all pages with that name in all sections. You can then open a page from the section you want with man SECTION PAGE_NAME.

Manpage sections

The various page sections are as follows and can be found from man man:

1. Executable programs or shell commands
2. System calls (functions provided by the kernel)
3. Library calls (functions within program libraries)
4. Special files (usually found in /dev)
5. File formats and conventions eg /etc/passwd
6. Games
7. Miscellaneous (including macro packages and conventions), e.g. man(7), groff(7)
8. System administration commands (usually only for root)
9. Kernel routines [Non standard]