Re: Checking executability for asynchronous commands

[Eli Schwartz]

On 12/28/20 8:15 AM, Greg Wooledge wrote:
> On Sun, Dec 27, 2020 at 08:02:49AM -0500, Eli Schwartz wrote:
> > I'm not sure I understand the question?
>
> My interpretation is that for an async *simple* command of the
> form   cmd args &   where cmd cannot be executed at all (due to
> lack of permissions, perhaps, or because the external program is
> not installed), they want bash to set $? to a nonzero value to
> indicate that the command couldn't even be started.
>
> I've seen similar requests several times over the years.
>
> The problem is that the parent bash (the script) doesn't know, and
> cannot know, that the command was stillborn.  Only the child bash
> process can know this, and by the time this information has become
> available, the parent bash process has already moved on.
>
> The only way the parent can obtain this information is to wait until
> that information becomes available.

Actually, I don't see why one could not circumvent the entire process, 
and do this instead

if cmd=$(type -P foo) && test -x "$foo"; then
    foo &
else
    echo "error: foo could not be found or is not executable"
fi

But I do get the initial premise of the thread. I don't get the 
*defense* being offered though.
The logic here seems to be completely bankrupt -- saying bash needs new 
features (that are not well thought out) so you don't "need" to include 
code to handle your intentions, is not a winning argument.

The OP seems to think that "people will occasionally forget to run 
`wait`", and wants to know if we "care" that people will forget and if 
Chet will add new features to bash in order to cater to these forgetful 
people. This is what I don't understand. Why should we care? The 
official advice is to run `wait` (or perform executability checks 
upfront, or whatever).

--
Eli Schwartz
Arch Linux Bug Wrangler and Trusted User

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