On 02/03/2018 17:33, Herbert Xu wrote:
On Fri, Mar 02, 2018 at 05:05:46PM +0100, Harald van Dijk wrote:
But in "${x+${y-}''}", the ' is the literal ' character. In "${x#${y-}''}",
the ' is a quote character. This part is hard. If the above is done simply
using another local variable, then the parse of the nested ${y-} would
clobber that variable.
I don't see why that's hard. You just need to remember whether
you're in a pattern context (i.e., after a %/%% or #/##). If you
are, then you need to go back to basesyntax instead of dqsyntax
until the next right brace.
Let me slightly modify my example so that the effect becomes different:
"${x#"${y-*}"''}"
When the parser has processed
"${x#"${y-
would the state be "in a pattern context", or "not in a pattern context"?
If the state is "in a pattern context", how do you prevent the next *
from being taken as unquoted? It should be taken as quoted.
If it stores "not in a pattern context", and the parser is processing
the last character in
"${x#"${y-*}
how can it reset the state to "in a pattern context"? Where could this
state be stored?
With arbitrarily deep nesting of variable expansions, I do not see how
you can avoid requiring arbitrarily large state, which gets difficult
with dash's non-recursive parser. Mind you, I do hope I'm missing
something obvious here!
Cheers,
Harald van Dijk
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