How to get shift+arrows and ctrl+arrows working in Vim in tmux?

Question

This is all in iTerm2 on OS X.

I used to have

export TERM='xterm-256color'

in my .bashrc. This meant Vim in tmux did use 256 colors.

And once I added

set -g xterm-keys on

then keyboard shortcuts with modifiers worked fine in Vim. Namely: shift+left/right that I mapped to switch Vim tabs, ctrl+up/down that I mapped to move ("bubble") lines, and shift+left/right which worked out of the box to jump by word in the command-line mode (e.g. when typing something like :e foo bar baz).

However, this setup had the problem that the Vim background color only shows behind text, as mentioned here.

So I removed

export TERM='xterm-256color'

from my .bashrc and instead put this in my .tmux.conf:

set -g default-terminal "screen-256color"

That fixed the Vim background color, but broke the keyboard shortcuts - they do unexpected things (move the cursor, delete text) instead.

By using ctrl+v to insert the verbatim output from the key combinations (as described here), I was able to work around it:

map [1;5A <C-Up>
map [1;5B <C-Down>
map [1;2D <S-Left>
map [1;2C <S-Right>
cmap [1;2D <S-Left>
cmap [1;2C <S-Right>

This makes the shortcuts work, but it doesn't feel like the right solution. Could anyone tell me what's happening here and how to fix it?

Answer 1

You need to set the tmux window option xterm-keys so that tmux will pass these keys through to its terminals. You probably want to put this in your ~/.tmux.conf:

set-window-option -g xterm-keys on

Vim will usually automatically set up its handling of these keys when TERM is xterm-something, but it skips this since TERM is screen-256color. You can manually configure these keys in your ~/.vimrc like this:

if &term =~ '^screen'
    " tmux will send xterm-style keys when its xterm-keys option is on
    execute "set <xUp>=\e[1;*A"
    execute "set <xDown>=\e[1;*B"
    execute "set <xRight>=\e[1;*C"
    execute "set <xLeft>=\e[1;*D"
endif

At least that way you do not have to map all the various combinations.

Answer 2

As explained here, disable Background Color Erase (BCE) by clearing the t_ut terminal option (run :set t_ut= in Vim and then press Control+L to refresh the terminal's display) so that color schemes work properly when Vim is used inside tmux and GNU screen.

This way, you can keep your TERM value as xterm-256color for proper key detection while also getting proper Vim color scheme rendering too! :-)