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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 18:30:16 +0100
User-agent: Mozilla/5.0 (X11; Linux i686; rv:10.0) Gecko/20120129 Thunderbird/10.0

On 02/28/2012 06:16 PM, Eric Blake wrote:
> On 02/28/2012 09:54 AM, John Kearney wrote:
>> On 02/28/2012 05:22 PM, Roman Rakus wrote:
>>> On 02/28/2012 05:10 PM, John Kearney wrote:
>>>> wrap it with single quotes and globally replace all single
>>>> quotes in the string with '\''
>>> single quote and slash have special meaning so they have to be 
>>> escaped, that's it. \'${var//\'/\\\'}\' it is not quoted, so
>>> it undergoes word splitting. To avoid it quote it in double
>>> quotes, however it changes how slash and single quote is
>>> treated. "'${var//\'/\'}'"
>>> Wasn't it already discussed on the list?
>>> RR
>> It was discussed but not answered in a way that helped.
> POSIX already says that using " inside ${var+value} is
> non-portable; you've just proven that using " inside the bash
> extension of ${var//pat/sub} is likewise not useful.
I'm just going for understandable/predictable right now.

>> Now I'm not looking foe a workaround, I want to understand it. 
>> Now you say they are treated special what does that mean and how
>> can I escape that specialness.
> By using temporary variables.  That's the only sane approach.
I do its just always bugged.

>> Or show me how without using variables to do this 
>> test=test\'string
>> [ "${test}" = "${test//"'"/"'"}" ] || exit 999
> exit 999 is pointless.  It is the same as exit 231 on some shells,
> and according to POSIX, it is allowed to be a syntax error in other
> shells.
I was going for || exit "Doomsday" i,e. 666 = 999 = Apocalypse.

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