(Dynamical) quantifier in search and replace

Question

In VIM, using search and replace like :%s/pat/repl/g, is it possible to have a quantifier in the replace part? As an example, replace every line matching pat by exactly 100 # without actually typing exactly 100 #'s into the command? Something like

s/pat/#\{100}/g

which, however, doesn't work for me.

More generally, is it possible to replace matches by a captured amount of characters? For example replace

This 3 is a text 5 
with some 2 numbers.

with

This XXX is a text XXXXX 
with some XX numbers.

using something like :%s/\(\d\)/X\{\1}/g?

Answer 1

You are searching for "sub-replace-expression":

:%s/\(\d\)/\=repeat('X', submatch(1))/g

With \= the replace string is a Vim script expression. Here the function repeat() is called. This functions returns a String that repeats the given String count times. The String is X and the count is the first match group.

See :help sub-replace-expression and :help repeat().