How can I get ‘n’ to go forward even if I started searching with ‘?’ or ‘#’?

Question

Vim has (at least) two sets of commands that search in opposite directions. Typing / and then a pattern will search forward through the document for the pattern; typing ? and then a pattern will search backward. The same relationship exists between the * and # commands.

What I don’t like is that these commands also set the search direction for the n and N commands. After using /, n goes forward through the document and N goes backward; after using ?, n goes backward and N goes forward. (In other words, n always goes in the same direction as the original search and N always goes in the other direction.)

How can I get n to go forward through the document, and N to go backward, regardless of which direction I started searching in?

Answer 1

You can change the behaviour of n and N to search consistently downwards/upwards by useing the following:

nnoremap <expr> n 'Nn'[v:searchforward]
nnoremap <expr> N 'nN'[v:searchforward]

Update: How does it work?

This uses expression-maps, which maps the lhs of the map to an expression that will be evaluated, everytime the lhs is encountered. See :h map-expression in the help.

What happens is, that the v:searchforward variable (which determines the internal state of which direction the last search was, see :h v:searchforward) is used as an index for the string in front of it. So in case of the first map, if the last search direction was forward, the n will be mapped to 'n' (index of 1, meaning return the second character) and if it was backward, the 'n' will be mapped to 'N' (because the v:searchforward variable is 0 and therefore the 'N' will be returned.

An alternative way to write those maps would be (which might be clearer):

nnoremap <expr> n (v:searchforward ? 'n' : 'N')
nnoremap <expr> N (v:searchforward ? 'N' : 'n')

There are also some plugins, that do that (ie the SearchRepeat plugin and possibly others as well).

Answer 2

Based on Christian Brabandt's solution I came up with

nnoremap <expr> n 'Nn'[v:searchforward].(&fdo=~'search\\|all'?'zv':'')
nnoremap <expr> N 'nN'[v:searchforward].(&fdo=~'search\\|all'?'zv':'')

These mappings also obey the foldopen setting

Answer 3

I’m using the SearchIndex plugin. To use Christian Brabandt’s answer but keep the plugin’s functionality of displaying the match number each time I type n or N, I put this in my vimrc:

nnoremap <silent><expr> n (v:searchforward ? 'n' : 'N') . ":SearchIndex<CR>"
nnoremap <silent><expr> N (v:searchforward ? 'N' : 'n') . ":SearchIndex<CR>"