Intro

The vim global command is a very powerful command, of course
in the comments sections many more will appear, just to give you
an idea on how useful it can be let's look to some situations.

create a new file based on a global pattern

• https://stackoverflow.com/a/56716368/2571881
• https://unix.stackexchange.com/a/257472/3157

Let's say we have this file:

this line contains cat
this contains dog
other nothing
more one with fish
this line contains cat
this contains dog

And we want a new file with the lines containing "dog" and delete them from the original file.

:g/\<dog\>/ .w! >> dog.txt | d

Copy lines with a pattern to a register

First let's clean the register we want to use

:let @a=''

Now we can copy the lines with a pattern to it

:g/pattern/y A
:g/pattern/ .,+5 y A 

The uppercase version of the register allow us to append content to a register, otherwise it will be overwrited.

To paste a register just

:0 put a

The above command says: at the line zero put the content of the register 'a'

" move TITLE down one line
:g/TITLE/ m+1   

" copy 'pattern' to <line number>
:g/pattern/t<line number> 

" erase even lines
:g/^/if line('.') % 2 == 0 | norm! cc

" erase odd lines
:g/^/if line('.') % 2 | normal! cc

" add a line before a pattern
:g/^wget/ normal O