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I'd like to write the following code:

function Normal(command)
    execute "normal!" a:command
endfunction
call Normal("\<C-O>")
call Normal("\<C-I>")

The first call to Normal succeeds, but the second throws an error:

E471: Argument required

Indeed, you get the same error if you enter the command :norm! ^I with the keystrokes:

:norm!SpaceCtrl-VCtrl-IEnter

I have a vague idea that the problem might be something to do with the fact that a Tab character is whitespace, but I'd like to know more precisely what's going on.

N.B. I've already worked around the issue by adding a count "1\<C-I>", so this is purely out of curiosity.

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  • Just to be clear, you already know command can't start with space, you want to know why it can't start with space?
    – dedowsdi
    Apr 5, 2019 at 12:15
  • @dedowsdi I'm afraid I don't understand your comment. My question is: Why doesn't :execute "normal! \<C-I>" do the same thing as pressing <Ctrl-I> in normal mode?
    – Rich
    Apr 5, 2019 at 12:26
  • 1
    Well, you knew command of :norm doesn't start with space(which include Tab), you knew \<C-I> is Tab, you knew you can add a count 1 to fix it, it confuses me.
    – dedowsdi
    Apr 5, 2019 at 12:44
  • @dedowsdi Thanks. Now I understand your comment. No, it wasn't clear to me that {commands} cannot start with a space also implies that {commands} cannot start with the byte 0x9. (But it looks as though you're right that it does.)
    – Rich
    Apr 5, 2019 at 13:03
  • ...which makes sense when you consider (which I had not) that the execute command might be in a Vimscript file--where tabs might be invisible--not necessarily on the command line.
    – Rich
    Apr 5, 2019 at 13:11

1 Answer 1

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3

If I guess then what's happening is, that the <c-i> gets expanded to a literal tab before inserting into the typeahead buffer. So Vim basically sees the command :norm! <tab>, which is not a valid command. I don't know a way around and even escaping did not work.

What works, is to use the feedkeys() command, e.g. :call feedkeys("\t", 'tn').

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