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Re: Sourcing a script from a pipe is not reliable


From: Jeremy
Subject: Re: Sourcing a script from a pipe is not reliable
Date: Thu, 10 Jan 2019 13:52:59 -0800

On Thu, Jan 10, 2019 at 11:59 AM Chet Ramey <address@hidden> wrote:

> On 1/10/19 2:52 PM, Jeremy wrote:
>
>> This command line should run forever:
>
>
>>   i=0; while [ "_$(echo echo '$1' | . /dev/stdin yes)" = "_yes" ]; \
>
>   do echo -n .; ((i++)); done; printf "\n%s\n" $i
>
>
>> When I run it, it usually terminates with $i much less than 1,000.
>
>
> >... The thing is I do not have control over which
> > versions of bash people use to run the script, so I need a workaround.
> >
> > ...
> > I am not happy with the obvious workaround of sourcing a file instead of
> > /dev/stdin.
>
> Have you considered reading stdin into a string (if it's one line) or an
> array (if it's more) and using `eval' on it? That obviously works better
> if it's one line, but could be made to work on multiple lines.
>
>
We are trying to determine if the current shell supports passing positional
arguments to a script sourced by dot (.), and we are trying to do it in a
way that will work under pretty much any shell. If you can show me how to
do that with eval, then that would be great, even though in general I hate
to ship a script that uses eval.

The best workaround I have come up with so far is to generate a more
complex script that outputs either "yes" or "no" and then retry if it gets
no output, but then I have to put a limit on retries to avoid a possible
infinite loop and handle the case where the loop terminates without an
answer. My hope is that if we understand the source of the bug we can
create a more straightforward work around.


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