5 ms·

Why would you implement system() at all?

• oguz-ismail 1y ago
  Because I don't want to implement a shell???
  • panzi 1y ago
    If you want to run a shell script, run a shell script. I.e. a text file with the executable bit set and a shebang. If you want to generate a shell script on the fly to then run it, take a step back and think about what you're doing.
    • oguz-ismail 1y ago
      Or I can just use system() because it's there and not going anywhere
• theamk 1y ago
  parse commands from config file? command-line arguments for hooks? https://news.ycombinator.com/item?id=44239036 https://news.ycombinator.com/item?id=44239036
  • panzi 1y ago
    I understand that it is convenient for running small snippets like that, but I don't really think it's worth the risk. And putting it into a config file is different, IMO. You don't get tempted to do some bad string interpolation there, because you can't, unless the config file format has support for that, but then I criticize that. If you need to pass things to such a snipped do it via environment variables or standard IO, not string interpolation. If you say you don't make such mistakes: Yeah, but people do. People that write the code that runs on your system.
    • theamk 1y ago
      But if you want a command-line option for hook, what are the alternatives? Force user to always create a wrapper script? that's just extra annoyance and if user is bad at quoting, they'll have the same problems with a script Disable hooks at all? that's bad functionality regression Ask for multiple arguments? this makes command-line parsing much more awkward.. I have not seen any good solutions for that. (The only exception is writing a command wrapper that takes exactly 1 user command, like "timeout" or "xargs".. but those already using argument vector instead of parsing)
      • frumplestlatz 1y ago
        You define a config file format that supports only the minimal syntax required to specify a multi-argument command (e.g. spaces separate arguments, arguments with spaces in them may be quoted or use backslashes to escape them). Then, you parse that out into a proper argument array and pass it to exec*/posix_spawn.
        • account42 1y ago
          So instead of a well known (i.e. POSIX) quoting semantics and existing tool support, you want to introduce your own ad-hoc format? No thanks.
          • frumplestlatz 1y ago
            A correct parser for the syntax I described can be written in less than a 100 lines of code — even in C. It’s a strict subset of the shell command language defined by POSIX, and it’s sufficiently expressive as to support specifying any argument array unambiguously. To correctly escape arbitrary shell syntax, not only do you need to handle the full POSIX syntax (which is quite complex) … https://pubs.opengroup.org/onlinepubs/9799919799/utilities/V3_chap02.html#tag_19_02 https://pubs.opengroup.org/onlinepubs/9799919799/utilities/V... … but you must also cover any bugs and undocumented/underspecified extensions implemented by the actual shell providing /bin/sh on every platform and platform version to which your code will be deployed. That’s not just difficult — it’s impossible, and everyone that has tried has failed, repeatedly. Leading to security bugs, repeatedly. https://gist.github.com/Zenexer/40d02da5e07f151adeaeeaa11af9ab36 https://gist.github.com/Zenexer/40d02da5e07f151adeaeeaa11af9... There’s a reason why we use parameterized queries instead of escaping to prevent SQL injection, and SQL syntax and parsing behavior is far more rigorously specified than the shell.