Syntax highlighting for not empty line starting with a space, but only if the previous line did not end with “=”

Question

I am currently working on a custom syntax highlighting for vim. I want to highlight lines starting with a space, but only if they contain any letters or numbers.

I could achieve this result with the syn match '^ .*.[a-zA-Z].*', but I want the highlight to be working only if the previous line does not end with a "=". Is this possible?

Thanks!

Answer 1

Here is a sample text to test the regex you want to build :

this line doesn't begin with a space
 this line begins with a space and the previous line doesn't end with =
 this line begins with a space and the previous line ends with =

The set of characters [a-zA-Z] can be expressed with the atom \a. So your regex can be rewritten like this :

^ .*.\a.*

Now your regex uses the ^ character, which stands for a beginning of a line. The problem is it can only be used at the beginning of the regex. To describe a beginning of line anywhere inside the regex, you have to use \_^.

Finally, you don't want the previous line to begin with the character =. This can be expressed with the following regex (in very magic mode) :

(\=\n)@<!

The end result is :

(\=\n)@<!\_^ .*.\a.*

Or if you want to be sure the very magic mode is enabled :

\v(\=\n)@<!\_^ .*.\a.*

Answer 2

Yes, it is.

O.k., now seriously. This is only for the starting space.

syntax match WhiteSpaceWithoutPrecedingEqualSign /=\@<!\n^ \S/hs=s+1,he=e-1
hi WhiteSpaceWithoutPrecedingEqualSign guibg=blue

This is for the line.

syntax match WhiteSpaceWithoutPrecedingEqualSign /=\@<!\n^ \S.*/hs=s+1
hi WhiteSpaceWithoutPrecedingEqualSign guibg=blue

• :h pattern
• :h syntax