On 15/03/2018 15:52, Herbert Xu wrote:
On Thu, Mar 15, 2018 at 12:41:10PM +0100, Harald van Dijk wrote:
It is if you want to do it the way POSIX specifies. You're adding a special
exception in the parser. I don't see how this approach can be extended to
handle the other examples in my mail:
I don't think it's exactly clear what POSIX says on this.
I don't think it's clear what POSIX means to say, but I do think it's
clear what it does say.
cat <<`one two`
ok
`one two`
Try this one:
cat << ${
${
bash/ksh93 both will get stuck forever until a right brace is
entered.
That's because POSIX specifies that after ${, everything up to the
matching }, not including nested strings, expansions, etc., is part of
the word. No exception is made when it spans multiple lines.
Another instance of this is
if false; then
echo ${
fi
}
fi
echo ok
This is accepted by bash, ksh, zsh and posh.
However, in this instance, I'm having trouble finding where, but IIRC,
POSIX says or means to say that it's okay to flag this as an invalid
parameter expansion at parse time even though the evaluation would
otherwise be skipped.
While other shells all behave the way dash does.
All? At least two others don't: yash rejects ${ as invalid because of
the missing parameter name. zsh agrees with bash and ksh that it should
look for the closing }.
Considering the fact that even if you closed the brace after
the newline bash would still be stuck forever,
That's because bash doesn't ever match multi-line heredoc delimiters.
Which is what POSIX technically requires:
"The here-document shall be treated as a single word that begins
after the next <newline> and continues until there is a line containing
only the delimiter and a <newline>, with no <blank> characters in between."
No single line will ever match a multi-line heredoc delimiter.
I think this
behaviour is suboptimal. ksh93 seems to do the right thing though.
Yes, I agree that multi-line heredoc delimiters are useful.
Another interesting thing to try is
cat << ${ foo
${
Also you can look at the quotes:
cat << "
"
IOW it's not clear that "word" in this context necessarily follows
the same rules used during normal tokenisation.
Quotes are clear: as far as they go, this *must* follow the same rules
used during normal tokenisation. Does any shell disagree?
cat << "A ' B"
ok 1
A ' B
echo ok 2
I expect this to print
ok 1
ok 2
and I'm not finding any shell that disagrees, not even dash. Do you have
an example of a shell that sees only "A as the heredoc delimiter, or one
that perhaps performs quote removal on the inner '?
For your example, does any shell, including dash, *not* treat this as a
multi-line heredoc delimiter consisting of a newline character (which
may or may not be matched by two blank lines, depending on the shell)?
Anyway, dash has had CHKEOFMARK since 2007 so this is just an
extension of existing behaviour.
This is definitely true: your patch, regardless of whether it matches
POSIX's requirements, is consistent with how dash has behaved for a long
time.
Cheers,
Harald van Dijk
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