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Re: Command substitution and errexit


From: DJ Mills
Subject: Re: Command substitution and errexit
Date: Mon, 15 Oct 2012 20:21:28 -0400

On Mon, Oct 15, 2012 at 8:08 PM, DJ Mills <address@hidden> wrote:
> while read -r attr state; do
>   if [[ $shellopts = *:"$attr":* ]]; then
>     set -o "$attr"
>   else
>     set +o "$attr"
>   fi
> done < <(set -o)

Erm, correction, that won't work for the first and last values in shellopts.
You could add colons to $shellopts ( [[ :$shellopts: = *:"$attr":* ]] ), or
use an array:

####
inarray() {
  local n=$1 h
  shift

  for h; do
    [[ $n = "$h" ]] && return
  done

  return 1
}

IFS=: read -ra opts <<<"$shellopts"
while read -r attr state; do
  if inarray "$attr" "address@hidden"; then
    set -o "$attr"
  else
    set +o "$attr"
  fi
done < <(set -o)
####

Or with bash 4, a more efficient version using an associative array:

####
declare -A setopts
IFS=: read -ra opts <<<"$shellopts"
for opt in "address@hidden"; do
  setopts[$opt]=1
done
unset opts

while read -r attr state; do
  if ((opts[$attr])); then
    set -o "$attr"
  else
    set +o "$attr"
  fi
done < <(set -o)
####

I know that the shell options are known beforehand, but it's always a good idea
to use safe coding practices. These methods are safe for any values in the
"$shellopts" string, whereas yours would break for spaces or regex characters.
You should also make sure to quote all of your expansions.

Would it be an option to create the needed environment in a subshell, where you
can set whatever options you'd like and not worry about them persisting?


By the way, if anyone has a more efficient way to create an associative array
like that other than that loop, I'd love to see it.



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