縦書きを横書きにするやつ、行はスペースで区切ること

example.txt

a e k k
i o a u
u   k k
    i e
      k
      o

tategaki.ts

const translate = (text: string) => {
  const res: string[] = [],
    lines = text.split(/[\r\n]+/).map((x) => x.split(/ {1,2}/));

  for (const line of lines) {
    for (let i = 0; i < line.length; i++) {
      res[i] = (res[i] ?? "") + line[i];
    }
  }

  return res;
};

const script = await Deno.readTextFile(Deno.args[0]);

console.log(translate(script).join("\n"));

つかいた

deno install -n tate2yoko -A https://gist.githubusercontent.com/ikasoba/141ce7937caa279d23b7d90ee3faade3/raw/e911508c2ee3f20c303fae43d13404cb7636816b/tategaki.ts

$ tate2yoko ./example.txt
aiu
eo
kaki
kukeko