Using a special key in function

Question

I am trying to remap <PageUp> key to call this function:

function! PageUp()
    let l:line = line('.')
    if(l:line != 1)
        if(l:line != winline())
            :set syntax=off
            <PageUp>
            :set syntax=on
        else
            normal! 1G
        endif
    endif
endfunction

but gvim complains that I cannot do it.

So what is the proper way to use the keys in a function ?

Answer 1

First of all, you use the PageUp key in Normal mode so the underlying functionality is a Normal mode command. You can't use such commands directly while in an Ex command-line or function/script. You need to use the Ex command :norm for this.

Further, to use "key codes" (:h key-codes) of non-printing characters like <PageUp> you need to construct the :norm command as an expression and pass it to the :exe command (see last paragraph of :h :norm).

That gives us:

:exe "norm \<PageUp>"

The double quotes are required as is the \ to escape the keycode and indicate that you want the special meaning not the literal string "<PageUp>".

(Note: Usually we want to use norm! instead of norm in order to avoid conflicts with mappings but that's not a critical element of this answer so omitted.)

Answer 2

To send special key to :normal, you need to get it's raw code by using "\<key>" notation.

exec "norm! \<PageUp>"

You can also use raw code directly if you want(not recommended, hard to read):

norm! <80>kP
        ^----------<80> is 0x80

<80>kP is raw code of <PageUp>, you can enter it like this in normal mode:

"="\<PageUp>"<cr>p
              ^----------press carriage return

If raw code of the key doesn't start with 0x80, it's the same as terminal code (not sure), you can use the :h i_CTRL-V to insert terminal code:

norm! <c-v><c-p>
       ^------------press ctrl-v ctrl-p

• :h :exec
• :h quote=
• :h string