#!/usr/local/bin/lua52
-- Replace all control characters with printable representations as in SciTECO.
-- These characters are printed in reverse using ANSI escape sequences.
-- This is especially useful as the diff textconv filter for Git as in
-- git config --global diff.teco.textconv tecat
local file = #arg > 0 and io.open(arg[1], 'rb') or io.stdin
while true do
	local buf = file:read(1024)
	if not buf then break end
	io.write((buf:gsub("[\00-\08\11\12\14-\31]", function(c)
		c = c:byte()
		return "\27[7m"..(c == 27 and '$' or '^'..string.char(c+0x40)).."\27[27m"
	end)))
end