Nrthugu

I want to execute an external program in lua. Usually this can be done with

os.execute("run '"..arg0.."' 'arg1' arg2")

The problem with this approach is if I want to pass user input as string to an external program, user input could be '; evil 'h4ck teh system' ' and the script from above would execute like this:

/bin/bash -c "run ''; evil 'h4ck teh system' '' 'arg1' arg2"

Another problem occurs when I have '$var' as argument and the shell replaces this with its environment variable. In my particular case I have something like [[program 'set title "$My Title$"']] – so nested strings – and program parses "$My Title$" (with escape sequences) differently than '$My Title$' (as it is). Because I want to set the title as it, the best way is to have arguments like this: 'My Title'. But now the command have to be:

os.execute([[run "set title '$My Title$'"]])

But now – as I said – $My will be replaced with an empty string, because the environment does not know any variable named $My and because, I never wanted it to be replaced.

So I am looking for the usual approach with

execv("run", {"set title '"..arg0.."'", arg1, arg2})

local safe_unquoted = "^[-~_/.%w%%+,:@^]*$"

local function q(text, expand)   -- quoting under *nix shells

   -- "expand"

   --    false/nil: $var and `cmd` must NOT be expanded (use single quotes)

   --    true:      $var and `cmd` must be expanded (use double quotes)

   if text == "" then

      text = '""'

   elseif not text:match(safe_unquoted) then

      if expand then

         text = '"'..text:gsub('["\]', '\%0')..'"'

      else

         local new_text = {}

         for s in (text.."'"):gmatch"(.-)'" do

            new_text[#new_text + 1] = s:match(safe_unquoted) or "'"..s.."'"

         end

         text = table.concat(new_text, "\'")

      end

   end

   return text

end



function execute_commands(...)

   local all_commands = {}

   for k, command in ipairs{...} do

      for j = 1, #command do

         if not command[j]:match"^[-~_%w/%.]+$" then

            command[j] = q(command[j], command.expand)

         end

      end

      all_commands[k] = table.concat(command, " ") -- space is arguments delimiter

   end

   all_commands = table.concat(all_commands, ";")  -- semicolon is commands delimiter

   return os.execute("/bin/bash -c "..q(all_commands))

end

Usage examples:

-- Usage example #1:

execute_commands(

   {"your/program", "arg 1", "$arg2", "arg-3", "~/arg4.txt"},

   {expand=true, "echo", "Your program finished with exit code $?"},

   {"ls", "-l"}

)

-- The following command will be executed:

-- /bin/bash -c 'your/program '''arg 1''' '''$arg2''' arg-3 ~/arg4.txt;echo "Your program finished with exit code $?";ls -l'

$arg2 will NOT be expanded into value because of single quotes around it, as you required.

Unfortunately, "Your program finished with exit code $?" will NOT be expanded too (unless you explicitly set expand=true).

-- Usage example #2:

execute_commands{"run", "set title '$My Title$'", "arg1", "arg2"}

-- the generated command is not trivial, but it does exactly what you need :-)

-- /bin/bash -c 'run '''set title '''''''$My Title$'''''' arg1 arg2'