Search and replace depending on capitalization of letters [duplicate]

Question

I would like to replace foo with bar and Foo with Bar. I can do

:s/Foo/Bar/g
:s/foo/bar/g

Can I do this in one command?

Answer 1

You could try this:

:s/\cfoo/\=submatch(0)[0] ==# 'F' ? 'Bar' : 'bar'/g

The replacement part of the substitution command is an expression which tests whether the first character of the pattern is F. If it is, the expression returns Bar, otherwise bar.