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Re: Command substitution and errexit


From: DJ Mills
Subject: Re: Command substitution and errexit
Date: Mon, 15 Oct 2012 20:08:10 -0400

On Mon, Oct 15, 2012 at 5:18 PM, Nikolai Kondrashov
<address@hidden> wrote:
> On 10/16/2012 12:08 AM, Greg Wooledge wrote:
>>
>> Sidestepping the direct question for a moment, you could use a temporary
>> file instead of a command substitution to store the output.  Then there
>> would be no subshell involved.
>
>
> Thanks, Greg. I don't like creating temporary files unnecessarily, so I went
> the route of using SHELLOPTS value instead and massaging it into a set of
> "set" calls on restore. Like this:
>
>     declare -r shellopts="$1"
>     declare -r on_pattern="^(${shellopts//:/|})\$"
>     declare attr
>
>     for attr in `set -o | awk '{print \$1}'`; do
>         if [[ $attr =~ $on_pattern ]]; then
>             set -o $attr
>         else
>             set +o $attr
>         fi
>     done
>
> Might need to do something with that awk invocation, though.
>
> Sincerely,
> Nick
>

Do not use for to iterate over the output of an unquoted command
substitution. Instead, use a while read loop.
See http://mywiki.wooledge.org/DontReadLinesWithFor and
http://mywiki.wooledge.org/BashFAQ/001

I also don't understand the point of using a regex like that, seems to
be way more complicated than it needs to be. A simple glob will
suffice here.

Assuming you're writing bash and not POSIX sh:

while read -r attr state; do
  if [[ $shellopts = *:"$attr":* ]]; then
    set -o "$attr"
  else
    set +o "$attr"
  fi
done < <(set -o)



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