--  The cat utility reads files sequentially, writing them to the standard
--  output.  The file operands are processed in command line order.  A single
--  dash represents the standard input.
--
--  The options are as follows:
--
--  -b	  Implies the -n option but doesn't number blank lines.
--
--  -e	  Implies the -v option, and displays a dollar sign (`$') at the
--	  end of each line as well.
--
--  -n	  Number the output lines, starting at 1.
--
--  -s	  Squeeze multiple adjacent empty lines, causing the output to be
--	  single spaced.
--
--  -t	  Implies the -v option, and displays tab characters as `^I' as
--	  well.
--
--  -u	  The -u option guarantees that the output is unbuffered.
--
--  -v	  Displays non-printing characters so they are visible.  Control
--	  characters print as `^X' for control-X; the delete character
--	  (octal 0177) prints as `^?' Non-ascii characters (with the high
--	  bit set) are printed as `M-' (for meta) followed by the character
--	  for the low 7 bits.
--
--  The cat utility exits 0 on success, and >0 if an error occurs.

require "getopt"

function visualizechar(char,visualizetabs,visualizenewline)
    local code = string.byte(char)
    local tab = (code == 9)
    local newline = (code == 10)
    if (code < 32 and not tab and not newline) or (tab and visualizetabs)
       or (newline and visualizenewline) then
	-- replace with ^x
	replacement = "^" .. string.char(code - 1 + string.byte("A"))
    elseif (code == 127) then
	replacement = "^?"
    elseif (code >= 128) then
	-- replace with M-something
	replacement = "M-" .. visualizechar(string.char(code - 128),true,true)
    else
	replacement = char
    end
    return replacement
end

function visualize(options,line)
	line = string.gsub(line, ".",
                function (ch) return visualizechar(ch,options.t,false) end)
	if options.e then line = line .. "$" end
	return line
end

function cat(options,f)
	local lineno, inputfile, prevlineempty
	if f == "-" then
		inputfile = io.stdin
	else
		inputfile = io.open(f)
	end
	if options.n or options.b then
		lineno = 1
	end
	local line = inputfile:read("*line")
	while line ~= nil do
		local lineempty = (line == "")
		if (not options.s) or not (lineempty and prevlineempty) then
			if options.v then line = visualize(options,line) end
			if options.n or (options.b and not lineempty) then
				io.write(string.format("%6d  ",lineno),line,"\n")
				lineno = lineno + 1
			else
				io.write(line,"\n")
			end
			if options.u then io.output():flush() end
		end
                prevlineempty = lineempty
	        line = inputfile:read("*line")
	end
        inputfile:close()
end

options = getopt(arg, "benstuv")
nfiles = arg.n
-- -e, -t imply -v
if (options.e or options.t) then options.v = 1 end
table.remove(arg, 0) -- remove program name
if nfiles == 0 then
	cat(options,"-")
else
	for i = 0,nfiles-1 do
		cat(options,arg[i])
	end
end
os.exit(0)