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From: Dan Douglas <ormaaj@gmail.com>
Newsgroups: gnu.bash.bug
Subject: Re: Parameter Expansion: Case Modification: ${var~} not documented
Date: Tue, 18 Aug 2015 12:43:14 -0500
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Cc: Isaac Good <isaacgood@gmail.com>, chet.ramey@case.edu
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On Tuesday, August 18, 2015 9:54:55 AM CDT Isaac Good wrote:
> Would you mind sharing the rational behind having it undocumented?

Since I like guessing: the syntax for parameter expansion operators is 
currently non-extensible, so the namespace of terse operators is in limited 
supply. New syntax should be extensible to suit future needs while keeping the 
language minimal. This is new syntax that adds one function that will be 
rarely used. I can think of better ways to use that operator.

The operators in use currently are already a disaster. We *really* could use a 
solution for the circumfix operators `!var[@]` and `!var[*]` that collide with 
the prefix `!` operator, and for reasons unknown don't interoperate with any 
of the other expansions such as array slicing / subscripting. I wouldn't want 
to add new (pointless) syntax before the fundamental problems are addressed.

-- 
Dan Douglas