Interactive search/replace regex in Vim?

I think you're looking for c, eg s/abc/123/gc, this will cause VIM to confirm the replacements. See :help :substitute for more information.

Mark Biek pointed out using:

%s/old/new/gc

for a global search replace with confirmation for each substitution. But, I also enjoy interactively verifying that the old text will match correctly. I first do a search with a regex, then I reuse that pattern:

/old.pattern.to.match
%s//replacement/gc

The s// will use the last search pattern.

Add the flag c (in the vim command prompt):

:%s/old/new/gc

will give you a yes/no prompt at each occurrence of 'old'.

Vim's built-in help offers useful info on the options available once substitution with confirmation has been selected. Use:

:h :s

Then scroll to section on confirm options. Screenshot below:

For instance, to substitute this and all remaining matches, use a.

I usually use the find/substitute/next/repeat command :-)

/old<CR>3snew<ESC>n.n.n.n.n.n.n.

That's find "old", substitute 3 characters for "new", find next, repeat substitute, and so on.

It's a pain for massive substitutions but it lets you selectively ignore some occurrences of old (by just pressing n again to find the next one instead of . to repeat a substitution).