From time to time I like to engage in a round of vimgolf. It can be enlightening.

How are they able to record all the keystrokes? That must be a vim feature. Anybody any idea how to do that. It could come in handy to record everything in certain circumstances.

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    I just found out that we have a pretty similar question here – statox Dec 6 '17 at 14:12

They probably use the built-in parameter -w, see :h -w:

-w {scriptout}  All the characters that you type are recorded in the file
        "scriptout", until you exit Vim.  This is useful if you want
        to create a script file to be used with "vim -s" or
        ":source!".  When the "scriptout" file already exists, new
        characters are appended.  See also |complex-repeat|.
        {scriptout} cannot start with a digit.
        {not in Vi}

Edit As @B Layer pointed out the actual code uses the -W parameter which is basically the same as -w but the log file is overwritten instead of appending the keystrokes to it (:h -W):

-W {scriptout}  Like -w, but do not append, overwrite an existing file.
        {not in Vi}
  • Good guess! It's -W not -w (see my answer) but still... – B Layer Dec 6 '17 at 12:38
  • @BLayer Well played I was too lazy to look at their code :-) I'll update with the doc for -W which is basically the same. – statox Dec 6 '17 at 12:40
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    Yep. Just append vs write. – B Layer Dec 6 '17 at 12:40
  • A (good) guess outvotes and gets accepted over a well-researched, fact-based answer? A grave injustice has been done. :( ... LOL – B Layer Dec 8 '17 at 19:46
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    'Tis a noble gesture. I humbly accept your vote, good sir or madam. Dilly dilly. – B Layer Dec 11 '17 at 20:40

I don't think it's quite that simple but you can look at the Ruby code yourself here:


I see a class for keylogging, for one.

Here's the command that is used to launch vim in lib/vimgolf/cli.rb:

 vimcmd = GOLFVIM.shellsplit + %W{-Z -n --noplugin --nofork -i NONE +0 
    -u #{challenge.vimrc_path} -U NONE -W #{challenge.log_path} #{challenge.work_path}}

@statox was (very nearly) right about -w outfile ... -W outfile, actually, which overwrites the file to which the typed characters are sent rather than appending to it. But as I said, not "quite that simple"...compare the contents of one of those files and what gets generated by the vimgolf tool. This is from an actual vimgolf problem...

-W output when copied then pasted here:

GI0. ý`gvgý`ZZ

Several non-printing characters got "lost in translation".

-W output as it appears on-screen:

^VGI0. ^[<80>ý`gvg^A<80>ý`ZZ

Well, that's kinda ugly.

vimgolf displayed/uploaded output:

<C-V>GI0. <Esc>gvg<C-A>ZZ

Ahh, that's better.

Update: I spent a few minutes looking a bit closer at things and have a couple new pieces of information.

First, the keylogger class keylog.rb that I mention above is indeed a major piece of the puzzle but it's actually fairly straightforward. The keycodes that Vim emits and which are saved in the -W log file are either one byte or three bytes (indicated by a first byte value of 0x80) and there is a hash map for each of the two sets.

The one-byte version maps the byte value to a string representation of the keycode such as 0 or g. The three-byte version similarly maps to a string (e.g. <Esc> or <C-V>) but using as the key the combined values of bytes two and three. There are some exceptions/corner-cases that are handled differently but the vast majority of keycodes are resolved through simple lookups in these two maps.

Seeing how basic the key logger code was I could tell something was wrong with what I was seeing in the keycode log files (such as the example pasted in above). It turns out I should have used the vimrc file required by VimGolf rules. In particular this line

set t_RV= 

results in the correct logging. The "appears on-screen" example above actually would look like this:

^VGI0. ^[gvg^AZZ

Now one can see the straight line from this "raw" string to VimGolf's rendered form.


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