el is a Lua expression evaluator with shell-friendly shortcuts, like ^string and print[[]

el.lua

#!/usr/bin/lua
-- Flatten ALL those tidy tables and add environment lookup
local tables = {math,io,os,string,bit32}
setmetatable(_G,{
	__index = function(t,key)
		for _,m in ipairs(tables) do
			local v = m[key]
			if v ~= nil then return v end
		end	
		return os.getenv(key)
	end
})

-- shell does NOT like print() so we have print[]
function bquote(a)
	local verb,aa = a:match '([%w_]+)(%b[])$'
	if verb then
		aa = aa:sub(2,#aa-1)
		return verb..'('..bquote(aa)..')'
	end
	return a
end

function quote(a)
	-- help with quoting strings
	local sa = a:match '^%^(.+)'
	if sa then return '"'..sa..'"' end
	return bquote(a)
end

--  f a b ... becomes f(a,b,...)
local expr = quote(arg[1])
local args = {}
for i = 2,#arg do
	args[i-1] = quote(arg[i])
end
if #args > 1 or type(_G[expr]) == 'function' then
	expr = expr..'('..table.concat(args,',')..')'
end

local f,e = load('return '..expr)
if e then
	print('error',e)
	os.exit(1)
end
-- not so easy to know if it's an error!
print(f())