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One can create non-rectangular Visual-Block selections using C-v$ on files with lines of non-equal length.

Is it possible to programmatically determine whether the last Visual Block selection was non-rectangular?

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A little crude but this works...

func! IsDollarBlock()
    let l:mode = char2nr(visualmode(""))
    if l:mode != 22
        echom char2nr(l:mode) . " is not block mode"
        return 0
    endif

    sil norm! gv"aygv$"by
    return @a == @b
endfunc

You can test with...

:echo IsDollarBlock()

(Assuming visual selection was not active)...first this checks whether the last visual selection was even block mode. If not it returns 0 (false). Otherwise it re-selects the visual selection and yanks into register "a", re-selects it again, issues $ and yanks into register "b". Then it compares the two registers and returns the comparison result (0/false or 1/true).

If you wanted to preserve the visual selection you could issue <Esc> or equivalent at the beginning of the function then put norm! gv as last command of the function.

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  • Alternate algorithm: if the lengths of the lines differ at all, it must be non-rectangular. Something like len(uniq(sort(map(lines, strlen)))) != 1
    – D. Ben Knoble ♦
    May 25, 2019 at 10:54
  • Hey DBK. My first thought was to use line lengths but you can make a non-rectangular selection without $ and the question is specifically about creating selections with $.
    – B Layer
    May 25, 2019 at 20:46

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