From: JJ <jjnoakes@...>
Date: 2008-01-09T13:20:10+09:00
Subject: Re: Ruby's Kernel::exec (and system and %x)

On Jan 8, 4:41 pm, thefed <fed...@gmail.com> wrote:
> On Jan 7, 2008, at 5:14 PM, Nobuyoshi Nakada wrote:
>
> >   cmd = "C:/Program Files/..."
> >   exec([cmd, cmd])
>
> > Citing from `ri exec':
> >      If the first argument is a two-element array, the first
> >      element is the command to be executed, and the second
> >      argument is used as the +argv[0]+ value, which may show up
> >      in process listings.
>
> But wouldn't that affect the program cmd, because it is having
> something passed to it?

No. This code

  exec([cmd, cmd])

is running cmd with no arguments. The second occurrence of "cmd" is
what is actually passed in to the process as its program name
(available to C programs via argv[0] in main(), for example).

So with the two-item list, there is no shell interpretation. To add
arguments, use

  exec([cmd, cmd], arg, arg)

but that is the same as

  exec(cmd, arg, arg)

simply because once you have at least two arguments to "exec", it
behaves in the no-shell fashion anyhow.

One could "trick" a program by running

  exec([cmd, "string"], arg, arg)

and the program would execute, but see "string" as how it was invoked.
This confuses some applications, but is possible.

-JJ