I found this useful setting form this post, which highlights trailing whitespaces :

highlight ExtraWhitespace ctermbg=grey guibg=grey
noremap <F10> :match ExtraWhitespace /\s\+$/<CR>

This works when I tap F10 but I also want the highlighting to go away when I tap F10 again. Typing :match works but I was wondering if this could be done from this keymap itself. I tried putting ! after match but that is not allowed.

1 Answer 1


You can get a List of all matches previously defined for the current window with the getmatches() function. By using an <expr> mapping, you can dynamically set a mapping based on the size of the List returned by getmatches() with a conditional expression.

Conditional expressions in Vimscript (often called ternary expressions in other languages) take the following form:

a ? b : c

where a, b, and c are expressions. If a evaluates to true, then the conditional expression as a whole evaluates to b, otherwise, it evaluates to c.

The following expression evaluates to ':match<CR>' if the length of the List returned by getmatches() is greater than zero, otherwise it will evaluate to ':match ExtraWhitespace /\s\+$/<CR>'.

len(getmatches()) > 0 ? ':match<CR>' : ':match ExtraWhitespace /\s\+$/<CR>'

Using an <expr> mapping allows you to evaluate an expression to determine the function of the mapping, rather than a static value. The result of the expression should be a string representation of the desired Ex commands.

So, putting our conditional expression together with our <expr> mapping, we can do the following:

noremap <expr> <F10> len(getmatches()) > 0 ? ':match<CR>' : ':match ExtraWhitespace /\s\+$/<CR>'

Relevant help:

:h :map-<expr>
:h getmatches()

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