Newline in sub-replace expression

Question

I've been trying to write a regex that turns the following structure

# Ignore this line

Foo
Foo

# Ignore this line too

into:

# Ignore this line

IF BAR THEN
    Foo
    Foo

# Ignore this line too

So far I have the following regex:

%s#\(\n\)\?\(\(Foo\n\)\+\)\(\n\)\?#\= submatch(1) . 'IF BAR THEN\r' . 
substitute(submatch(2), 'Foo', '    &', 'g') . submatch(4)#gc

Which gives me:

# Ignore this line

IF BAR THEN\r    FOO
    Foo

# Ignore this line

I have tried using \n, <CR>, ^M but none seem to have the desired output. Please advise!

Answer 1

The problem is that you're using a literal string (delimited by single quotes) where you want to use an escape character \r.

Replace them with double quotes to fix:

... "IF BAR THEN\r" ...

(See :help string.)