Why does the command ":g x" show all lines matching the last search?

Question

I accidentally stumbled on a solution for a problem I had: I wanted to get an overview over all occurrances of the word under the cursor, after I used # to find them individually.

For some reason I guessed the command :g % and it did what I wanted. But I could not find an explanation of this, neither by reading :help :g nor :help g nor :help % nor :help pattern nor :help cword.

I experimented some more with this and I figured out

• that it had nothing to do with the cursor position and it would just repeat the last search,
• that I could replace the % with any single character (or at least, all that I tried worked), but there had to be one, and there had to be at least one space between :g and that character.

For example, :g a, :g x, :g #, :g c all worked.

Typing one more character would use this as a start of a new search apparently.

Where can I find the documentation for this invocation? :help :g shows :g/{pattern}/[cmd] and does say that the / can be replaced by a different character, so I figured it could be a space, but then the syntax should be

:g<space>{pattern}<space>[cmd]

and I understand that the default cmd is :p which prints the matching lines, but I still don't understand why the last search pattern is inserted automatically and what the relevance of that trailing other character (%, a, x above) is.

I'm using Vim 8.2.2434.

Answer 1

The way I understand it:

:g[global] /{pattern}/ [cmd]

1. You can have spaces between the global keyword and the pattern separator
2. The pattern separator can be any non alphanumeric character (except \, | or ")
3. The ending pattern separator is optional if not cmd is to be specified
4. If the pattern is empty the last pattern (/ register) is used
5. If the cmd is not specified p (print) is used

With these rules :g# is equivalent to :g##p or :g//p or :g#Ctrl-r/#p