Vim find and replace with filename as variable

Question

Is it possible to use vim find and replace to replace a variable with the current filename? for example, fancyFileName.txt contains

this is the VARIABLE to replace in this fancyFileName.txt

and I am trying to use something like :%s/VARIABLE/expand(%)/ to get

this is the fancyFileName.txt to replace in this fancyFileName.txt

Answer 1

As pointed out in other answers, :help sub-replace-special, and :help \=, you can use any expression as the replacement text like so:

:%substitute/\<VARIABLE\>/\=expression/g

In your case:

:%substitute/\<VARIABLE\>/\=expand('%')/g

Answer 2

Assuming you have defined VARIABLE as a global Vim Script variable like this:

:let g:VARIABLE='fanceFileName.txt'

you can then use:

%s/\<VARIABLE\>/\=get(g:, submatch(0), '')/g

This uses the special atom \= to evaluate the following as a VimScript expression using get(g:, 'VARIABLE', '') to access the variable from the global dictionary :g

See also :h sub-replace-special