This first edition was written for Lua 5.0. While still largely relevant for later versions, there are some differences.
The fourth edition targets Lua 5.3 and is available at Amazon and other bookstores.
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4.3.3 – repeat

As the name implies, a repeat-until statement repeats its body until its condition is true. The test is done after the body, so the body is always executed at least once.

    -- print the first non-empty line
      line =
    until line ~= ""