I considered help-bash for this, but I settled on bug-bash since it's about
an in-development version.
$ colors=(red green blue)
$ printf '%s\n' "${colors[*]@a}"
a a a
Which is consistent with the documentation:
a The expansion is a string consisting of flag values
representing parameter's attributes.
If parameter is @ or *, the operation is applied to each
positional parameter in turn, and the expansion is the
resultant list. If parameter is an array variable
subscripted with @ or *, the case modification operation is
applied to each member of the array in turn, and the
expansion is the resultant list.
But would seem to imply that each element is itself an array when they are
clearly instead elements of an array. Without the subscript, only one "a"
is output which is also consistent with the documentation.
For comparison:
$ printf '%s\n' "${colors[*]@A}"
declare -a colors=([0]="red" [1]="green" [2]="blue")
$ printf '%s\n' "${colors@A}"
declare -a colors='red'
Only one "-a" (of course). Curiously, when there's no subscript, only a
single element is output which is consistent with long-standing Bash
behavior, but there's that "-a" which is correct. I suppose it's a case of
you get what you ask for.
$ neutral=gray
$ printf '%s\n' "${neutral[*]@A}"
neutral='gray'
$ printf '[%s]\n' "${neutral[*]@a}"
[]
In the "gray" example, the same result is given when the subscript is
omitted, of course.
I guess the point I'm trying to get to is that I don't see
how "${colors[*]@a}" or "${colors@A}" are useful whereas their opposites
are ("${colors@a}" and "${colors[*]@A}") regardless of whether the
parameter is an array or scalar. By the way, subscripting using "@" with
these transformations also doesn't seem to be useful.
It may be that this is not a matter for changing the Bash code or
documentation but that it's necessary to consider these behaviors when
making good coding practice choices.
To tell me what attributes this name has: "${var@a}"
To tell me how to reproduce this name and its contents: "${var[*]@A}"
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