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Re: Inconsistent quote and escape handling in substitution part of param

From: John Kearney
Subject: Re: Inconsistent quote and escape handling in substitution part of parameter expansions.
Date: Tue, 28 Feb 2012 23:40:10 +0100
User-agent: Mozilla/5.0 (X11; Linux i686; rv:10.0) Gecko/20120129 Thunderbird/10.0

On 02/28/2012 11:23 PM, Chet Ramey wrote:
> On 2/28/12 5:18 PM, John Kearney wrote:
>> 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.
> Maybe, but that's not how things work in practice.  Should the following
> expansions output the same thing?  What should they output?
> bar=abc
> echo ${foo:-'$bar'}
> echo "${foo:-'$bar'}"
> Chet

and truthfully with thr current behavior Id' almost expect this  behavior.

but to be honest without trying it out I have no idea and that is the
problem now.

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