Re: Inconsistent quote and escape handling in substitution part of parameter expansions.

[John Kearney]

On 02/28/2012 11:07 PM, Chet Ramey wrote:
> On 2/28/12 4:28 PM, John Kearney wrote:
>> 
>> On 02/28/2012 10:05 PM, Chet Ramey wrote:
>>> On 2/28/12 12:26 PM, John Kearney wrote:
>>> 
>>>> But that isn't how it behaves. "${test//str/"dddd"}"
>>>> 
>>>> because str is replaced with '"dddd"' as such it is treating
>>>> the double quotes as string literals.
>>>> 
>>>> however at the same time these literal double quotes
>>>> escape/quote a single quote between them. As such they are
>>>> treated both as literals and as quotes as such 
>>>> inconsistently.
>>> 
>>> I don't have a lot of time today, but I'm going to try and
>>> answer bits and pieces of this discussion.
>>> 
>>> Yes, bash opens a new `quoting context' (for lack of a better
>>> term) inside ${}.  Posix used to require it, though after
>>> lively discussion it turned into "well, we said that but it's
>>> clearly not what we meant."
>>> 
>>> There are a couple of places in the currently-published version
>>> of the standard, minus any corregendia, that specify this.  The
>>> description of ${parameter} reads, in part,
>>> 
>>> "The matching closing brace shall be determined by counting
>>> brace levels, skipping over enclosed quoted strings, and
>>> command substitutions."
>>> 
>>> The section on double quotes reads, in part:
>>> 
>>> "Within the string of characters from an enclosed "${" to the
>>> matching '}', an even number of unescaped double-quotes or
>>> single-quotes, if any, shall occur."
>>> 
>>> Chet
>> 
>> yhea but I think the point is that the current behavior is
>> useless. there is no case where I want a " to be printed and
>> start a double quoted string? and thats the current behavior.
>> 
>> 
>> Not so important how you treat it just need to pick 1. then you
>> can at least work with it. Now you have to use a temp variable.
>> 
>> 
>> as a side note ksh93 is pretty good, intuitive ksh93 -c
>> 'test=teststrtest ; echo "${test//str/"dd dd"}"' testdd ddtest 
>> ksh93 -c '( test=teststrtest ; echo ${test//str/"dd '\''dd"} )' 
>> testdd 'ddtest
> 
> The real question is whether or not you do quote removal on the
> stuff inside the braces when they're enclosed in double quotes.
> Double quotes usually inhibit quote removal.
> 
> The Posix "solution" to this is to require quote removal if a
> quote character (backslash, single quote, double quote) is used to
> escape or quote another character.  Somewhere I have the reference
> to the Austin group discussion on this.
> 

1${A:-B}2

Logically for consistancy having double quotes at position 1 and 2
should have no effect on how you treat string B.


or
consider this
1${A/B/C}2

in this case its even weirder double quotes at 1 and 2 has no effect
on A or B but modifies how string C behaves.