On 11/5/18 4:42 PM, Great Big Dot wrote:
> Description:
> The parameter expansion "${!var[@]}" expands to the indices of an array
> (whether linear or associative). The expansion "${var-string}"
> returns "${var}" iff var is set and 'string' otherwise. These two
> features do not play well together:
You seem to have neglected a significant section of the documentation:
"If the first character of parameter is an exclamation point (!), and
parameter is not a nameref, it introduces a level of indirection. Bash
uses the value formed by expanding the rest of parameter as the new
parameter; this is then expanded and that value is used in the rest of
the expansion, rather than the expansion of the original parameter.
This is known as indirect expansion. The value is subject to tilde
expansion, parameter expansion, command substitution, and arithmetic
expansion. If parameter is a nameref, this expands to the name of the
parameter referenced by parameter instead of performing the complete
indirect expansion. The exceptions to this are the expansions of
${!prefix*} and ${!name[@]} described below. The exclamation point
must immediately follow the left brace in order to introduce indirec-
tion."
> $ declare -a -- array=([0]='helloworld')
> $ printf -- '%s\n\n' "${!array[@]-Warning: unset}"
> Warning: unset
This happens to "work" because there is a single array element set, and it
expands to a single word.
--
``The lyf so short, the craft so long to lerne.'' - Chaucer
``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU c...@case.edu http://tiswww.cwru.edu/~chet/
