Vim regex: add line above all lines not starting with "#"

Question

I have a text file with a structure like this:

The quick  
#a comment
brown 
fox jumps  
#another comment
over  
the 
lazy
#yet another comment
dog

So each line either contains "normal" text or a comment starting with "#". I want this text to be replaced using regex, so that each "text"-line gets a comment line above it. The result should be something like:

#auto comment
The quick  
#a comment
brown 
#auto comment
fox jumps  
#another comment
over  
#auto comment
the 
#auto comment
lazy
#yet another comment
dog

However, I'm not able to create a working regex although I spent really much time. There's always at least one special case where my regex fails. The best one I was able to create is:

:%s/^\([^#].*\)\n\([^#].*\)$/\1\r#auto comment\r\2/g

This one works perfectly fine (except for the first line), if I run it twice. But running it only once skips some lines, e.g. I get this result:

The quick
#a comment
brown
#auto comment
fox jumps
#another comment
over
#auto comment
the
lazy
#yet another comment
dog

Notice that there's no line inserted between "the" and "lazy". The reason for this is, that the term "the" is a part of the regex group and part of the replaced text and so it won't be parsed by regex again.

Is there any possibility (well I bet there is and I'm just not able to find it...) to solve this issue? I realize that checking the first line is another problem, too. It would be great if this could be recognized, too, however this is currently not my main focus of attention.

Answer 1

You can use a negative look-behind, \@<!, to ensure the previous line is not a comment.

%s/\(^#.*\n\)\@<!\_^[^#]/#auto comment\r&

For more information see:

:h /\@<!
:h /\_^
:h s/\\&

Answer 2

([^#\n]+\n#[\w ]+?\n[^\n]+(?:\n|$))|^([^\n]+\n)

Try this.Replace by #auto comment\n$1$2.See demo.

http://regex101.com/r/lZ5mN8/24

Answer 3

Use: :%s/^\([^#].*\)/#auto comment\r\1/g

Then run: :%s/^\(#.*\)\n#.*/\1/g

OR :%s/^\([^#].*\)/#auto comment\r\1/g | %s/^\(#.*\)\n#.*/\1/g