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*From*: Robert Elz
*Subject*: Re: ${p+\"$p\"}
*Date*: Mon, 21 Jan 2019 23:38:22 +0700
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(...)
> With the quotes, most other shells produce the output reported
> from dash (that includes ksh93, yash, ...) zsh just says it iis
> a parse error, which is probably a rational choice!
> Nothing else I tested produces what bash does, which does seem
> to be a kind of odd pair of results.
That is quite inexact, there are four groups:
heirloom sh : "A" \"A\" \\"A\\" \\\"A\\\"
ash : A \"A\" \A\ \\"A\\"
dash : A \"A\" \A\ \\"A\\"
b43sh : A \"A\" \A\ \\"A\\"
b44sh : A \"A\" \A\ \\"A\\"
posixbash : A \"A\" \A\ \\"A\\"
yash : A "A" \A\ \"A\"
y2sh : A "A" \A\ \"A\"
posh : A "A" \A\ \"A\"
lksh : A "A" \A\ \"A\"
mksh : A "A" \A\ \"A\"
ksh93 : A "A" \A\ \"A\"
attsh : A "A" \A\ \"A\"
zsh/sh : ./t.sh:7: parse error
zsh/ksh : ./t.sh:7: parse error
zsh : ./t.sh:7: parse error
But yes:
> But this is an area that is a monumental mess, and the only rational
> choice is to find some workaround which does not involve putting
> a " inside a var expansion inside a here doc.
Maybe:
p=A
q='"'
cat <<_EOF_
${p+$q$p$q} ${p+\\$q$p\\$q}
_EOF_
Which yields "A" \"A\" in all shells tested (except heirloom bourne shell).
Or, even simpler (depending on use):
echo ${p+"$p"} ${p+\"$p\"} ${p+\\"$p\\"} ${p+\\\"$p\\\"}
