There is a python3 variant in this thread [1], but if that is not "standard enough" (as someone else may have mentioned bash itself is not POSIX), this awk would also work { Warning - this awk is 1000s of times faster than the bash. So, you really probably want that sleep { and sure 100s of times faster yet may be possible. } }:

    #!/usr/bin/awk -f
    BEGIN {
      # Split on spaces so multi-byte utf8 works
      nText  = split("♥ P E A C E ♥ F O R ♥ A L L", tmp, " ")
      for (i = 0; i < nText; i++) text[i] = tmp[i + 1]
      color0 = 12; color1 = 208  # xterm-256 color cube range
      nColor = color1 - color0   # Could be a pretty gradient
      w = ENVIRON["COLUMNS"]; if (w == "") w = 80
      h = ENVIRON["LINES"];   if (h == "") h = 24
      freq = 0.2
      for (t = 0; 1; t++) {
        x     = int(w/2 + w/4*sin(t*freq) + 0.5)  # x pos ~ sine
        color = color0 + int((nColor*t)/h)%nColor # cycle colors
        ch    = text[t % nText]                   # cycle chars
        printf("%*s\033[38;5;%dm%s\033[m\n", x, "", color, ch)
        fflush()
      # system("sleep 0.1") # awk has no builtin sleep
      }
    }

As to "bug reports", the T-shirt published script also fails with LC_ALL=C for me as mentioned else-thread.

FWIW, I think ancient practice to reach for `bc` instead of `awk` or even the arithmetic built into shells often annoys. The only reason I keep `bc` installed at all is to compile Linux kernels. Someone had some patch set to Linux to eliminate this very dependency many years ago now.

[1] https://news.ycombinator.com/item?id=48830669

Broken seems a little hyperbolic, it has an implicit dependency on a standard POSIX tool.