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Is this even possible?

I'd like to run a command but capture its stdout and stderr as separate variables. Currently I'm using set -l var (cmd), which leaves stderr untouched. I can do set -l var (cmd ^&1) which will merge stdout and stderr into var, but then I can't easily separate them again.

Is there any way to get var and var_err to hold stdout and stderr from cmd?

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begin; cmd ^|read -z err; end |read -z out

From fish-shell/fish-shell #2463,

An issue in your fish example is that it redirects [stdout] of both [cmd] and [read], so if the latter prints anything, it'll be carried through the pipe.

But I don't think read should ever print anything (especially to stdout) in the normal case, so this should be fine.

Edit: If the exact semantics of set var (cmd) are needed, that can be achieved using set var (printf '%s' $out) and set var_err (printf '%s' $err)

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The simplest method would be to redirect one of the streams to a file:

set tmpf (mktemp)
trap "rm $tmpf" EXIT

set var (cmd ^ $tmpf)
set var_err (cat $tmpf)
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