add command runner util

lib/util.lua

@@ -32,4 +32,15 @@ function M.ls(dir)
 	return t
 end
 
+function M.run(cmd)
+	cmd = cmd or "echo nil"
+	local p = io.popen(cmd)
+	if not p then
+		return nil
+	end
+	local r = p:read("*a"):gsub("%s+$", "")
+	p:close()
+	return r
+end
+
 return M