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Date: Fri, 13 Nov 2015 20:18:00 -0800
From: Ray Andrews <rayandrews@eastlink.ca>
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To: Zsh Users <zsh-users@zsh.org>
Subject: capturing stderr to variable.
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Gentlemen:

'highlight' seems to have no return value. If you feed it a file who's 
type it does not recognize, it sends a message to stderr. To create a 
test for that, I'm doing this:

    $ highlight $filename 2> /tmp/highlight_err
    [ -s "/tmp/highlight_err" ] &&
    echo="Highlighting is active, but the file is not recognized."
    rm /tmp/highlight_err > /dev/null

... which is clumsy.  Researching it, I find that there's no simple way 
to redirect stderr to a variable, or to some other way of capturing the 
error condition. Suggestions involve things like:

     ... 2>&4 1>&3; } 2>&1 )

... which I'd not use anyway for clarity's sake.  Any suggestions?  I 
was wondering, since redirection and piping are (I believe) at about the 
same level of parsing, one might suppose that " ... 2| " would be 
legal.  That is to say that we could sent stderr to a command as well as 
to a file.