The following script removes all comments (single line or multi line) from 5 types of files that I use mostly: JavaScript, HTML, XML, CSS and Lua.

formats={
	["js"]={
		name="JavaScript",
		single="//.-\n",
		multi="/%*.-%*/"
	},
	["xml"]={
		name="XML",
		single=nil,
		multi="<!--.--->"
	},
	["html"]={
		name="HTML",
		single=nil,
		multi="<!--.--->"
	},
	["css"]={
		name="CSS",
		single=nil,
		multi="/%*.-%*/"
	},
	["lua"]={
		name="Lua",
		single="--.-\n",
		multi="/%[%[.-%]%]/"
	},

}
---Gets a valid compilable javascript code and removes its comments
-- @note the javascript code should be ready to compile that is: there are no syntax
-- errors whatsoever. Otherwise the behavior of this function is unpredictable.
-- @param txt the compilable javascript code
-- @param patt the pattern table from format table. See how it's called from removeCommentsFile()
-- @return a text string the semantically behaves the same as the txt that was passed
-- to the function but doesn't have comments
function removeComments(txt,patt)
	--remove all multi-line comments
	if patt.multi then
		txt=txt:gsub(patt.multi,"\n")
	end
	--remove all single-line comments
	if patt.single then
		txt=txt:gsub(patt.single,"\n")
	end

	txt=txt:gsub("\n[%s]*","\n")  --remove all soaces at the start of lines
	txt=txt:gsub("[%s\n]*\n","\n")--remove all empty lines and all spaces at the end of lines
	txt=txt:gsub("^\n","")        --remove first empty new line
	txt=txt:gsub("\n$","")        --remove last empty new line
	return txt
end

---Opens a file and detects its extension before passing the contents to removeComments()
function removeCommentsFile(fileName)
	local f=io.open(fileName,"r")
	local txt=f:read("*a")
	local extension=fileName:match("%.(.-)$")
	if not extension then
		return nil,"Could not find extension for file '"..fileName.."'"
	end
	extension=extension:lower()
	if formats[extension] then
		print("Removing comments from '"..fileName.."' (a "..formats[extension].name.." file)")
		return removeComments(txt,formats[extension])
	else
		return nil,"This file is not recognized: '"..fileName.."'"
	end
end

for k,v in ipairs(arg) do
	print(removeCommentsFile(v))
end