Case preserving substitute in Vim

Question

Use abolish.vim:

:%S/badjob/goodjob/g

I don't know if this is the kind of solution you're looking for... but i've used this: keepcase.vim

There's no support otherwise in vim...

sure u can

:s/\cbad/\= strpart(submatch(0), 0 ,1) == toupper(strpart(submatch(0), 0, 1)) ? "GOOD" : "good"/

ps. i'm guessing keepcase.vim encapsulates some similar logic :)

You can just paste and adapt this:
_{(Of course, if you do this from time to time, you will want a plugin instead of this monstrosity. But for some who are in a hurry and only need it once, this is a quick hack for your pasting pleasure:)}

:%s/\cbad\zejob/\= ( submatch(0)[0] is# toupper(submatch(0)[0]) ? 'G' : 'g' ) . ( submatch(0)[1] is# toupper(submatch(0)[1]) ? 'OOD' : 'ood' )

Apart from the search pattern, you have to edit the four 'strings' in the replacement code: Edit the parts in bold:

:%s/\cbad\zejob/\=
( submatch(0)[0] is# toupper(submatch(0)[0]) ? 'G' : 'g' ) .
( submatch(0)[1] is# toupper(submatch(0)[1]) ? 'OOD' : 'ood' )

Don't use this 'orange' version for pasting, since its linebreak characters will also break the command.

/\ze is vim regex syntactic sugar for marking a positive lookahead: The pattern after \ze is checked for, but not substituted.

is#?? Let me explain… (If interested.)

# (also in ==# and others) enforces case sensitivity. Otherwise, with :set ignorecase (which I use, because that is required for the useful :set smartcase), vim will consider 'a' == 'A'!!

Crazy as it is, we really should account for it: Because it is user-settings-dependent, == should NEVAR be used! (Except where that would actually be what you want.) I will even follow the recommendation to use ==# when comparing integers: http://learnvimscriptthehardway.stevelosh.com/chapters/22.html#code-defensively

is# instead of ==# is another way of coding defensively: It improves type safety: http://google.github.io/styleguide/vimscriptguide.xml?showone=Type_checking#Type_checking
It should be used when comparing against a string literal.

'single-quoted' instead of "double quoted" strings are another good practice: http://google.github.io/styleguide/vimscriptguide.xml?showone=Strings#Strings

_{HT @fc. - this answer builds on their answer, fixing a few shortcomings.}