Re: surprise with echo

[Bart Schaefer <schaefer@xxxxxxxxxxxxxxxx>]

On Dec 18,  5:24pm, Ray Andrews wrote:
}
} Why should it do that? It's very cool what it permits
} as explained in 'the book' p. 288, but is the above
} part and parcel of that?

The doc spells this out explicitly:

RC_EXPAND_PARAM (-P)
     Array expansions of the form `FOO${XX}BAR', where the parameter XX
     is set to (A B C), are substituted with `FOOABAR FOOBBAR FOOCBAR'
     instead of the default `FOOA B CBAR'.  Note that an empty array
     will therefore cause all arguments to be removed.

} Can that be prevented?

Only by turning off the option, or by doing e.g. ${@:-''} so that the
expansion is the empty string rather than the empty array.

} Is this a feature?

It's how array expansion works in the "rc" shell, which is the source
from which this behavior is borrowed.  There's probably an "rc" list
somewhere where you might get an explanation.