Re: [BUG] [PATCH]: run-command.c

From: Jeff King <peff@peff.net>
Date: Oct 21, 2016, 09:00 UTC
Message-ID: <20161021090029.glr5u6gwrxluavir@sigill.intra.peff.net>
In-Reply-To: <20161021055013.GA31554@dimstar.local.net>

On Fri, Oct 21, 2016 at 04:50:13PM +1100, Duncan Roe wrote:

Show 16 quoted lines

> For example, if .git/config has this alias (the sleep is to leave time to
> examine output from ps, &c.):
> 
> [alias]
> 	tryme = "!echo $PWD;sleep 600"
>
> [...]
> 16:42:06$ ps axf|grep -A2 trym[e]
>  2599 pts/4    S+     0:00      \_ git tryme
>  2601 pts/4    S+     0:00          \_ /bin/sh -c echo $PWD;sleep 600 echo $PWD;sleep 600
>  2602 pts/4    S+     0:00              \_ sleep 600
> 16:42:45$ cat /proc/2601/cmdline | xargs -0 -n1 echo
> /bin/sh
> -c
> echo $PWD;sleep 600
> echo $PWD;sleep 600

This duplicated argument is expected and normal. The arguments after "-c whatever" become positional parameters $0, $1, etc. The actual script arguments start at "$1", and "$0" is typically the "script name". So you have to stick some placeholder value in the "$0" slot, so that the sub-script can find the actual arguments. E.g., try:

  sh -c '
    for i in "$@"; do
      echo "got $i"
    done
  ' one two three

it will print only:

  got two
  got three

But if you stick a placeholder there, it works:

  sh -c '
    for i in "$@"; do
      echo "got $i"
    done
  ' placeholder one two three

The value of the placeholder does not matter to the shell. But it is accessible to the script inside via $0:

  sh -c '
    echo "\$0 = $0"
    echo "\$1 = $1"
    echo "\$2 = $2"
    echo "\$3 = $3"
  ' placeholder one two three

Since our script does not have a filename, we just stick the script contents there (which is really just a convention, and one I doubt anybody is really relying on, but there's no point in breaking it now).

Show 12 quoted lines

> --- a/run-command.c
> +++ b/run-command.c
> @@ -182,8 +182,8 @@ static const char **prepare_shell_cmd(struct argv_array *out, const char **argv)
>  		else
>  			argv_array_pushf(out, "%s \"$@\"", argv[0]);
>  	}
> -
> -	argv_array_pushv(out, argv);
> +	else
> +		argv_array_pushv(out, argv);
>  	return out->argv;
>  }

Try running "make test" with this. Lots of things break, because we are not sending the positional parameters to the shell script at all.

If we just cared about the positional parmeters, we _could_ do something like:

  if (argv[0]) {
	argv_array_push(out, "sh");
	argv_array_pushv(out, argv + 1);
  }

That would omit "$0" entirely when we have no positional parameters (and the shell generally fills in "sh" there itself), and provide a dummy "sh" value when we need to use it as a placeholder.

But again, there's no real value in breaking the existing convention.

-Peff