On 11/12/2018 1:32 PM, Grisha Levit wrote:
When an array A has non-zero elements but the expansion of "${A[*]}" is
still
a null string, it is not treated as such for purposes of ${var:-X} expansion
(though $* is treated as null in the same circumstance).
$ A=(''); set -- ''
$ echo "<${A[*]:-X}>" "<${*:-X}>"
<> <X>
----
Ah, a null string != empty. Example:
A=()
declare -p A
declare -a A=()
A=('') #null string
declare -p A
declare -a A=([0]="") #a string is still a string, even if empty
Related:
FWIW, below, "IFS=" sets IFS to an empty string, like
IFS=''
$ IFS=
$ A=('' ''); set -- '' '';
Typing in lines to echo the size of A and shell params:
echo "=$#" ; echo number of parameters set by "set - '' ''"
=2
echo "size of A=${#A[@]}"
size of A=2
$ echo "<${A[*]:-X}>" "<${*:-X}>"
<> <X>
---
Going to use "«»" instead of "<>" cuz <> are shell chars that
need quoting ( otherwise: bash: syntax error near unexpected token `<' ).
First, your echo:
echo "«${A[*]:-X}»" "«${*:-X}»"
«» «X» (#same)
and w/o the quotes:
echo «${A[*]:-X}» «${*:-X}»
« » « »
---
Notice adding quotes around your vars can change what is
echo'ed. Looks like the output-separator ' ' (space) is
embedded in the '*'s of both expressions, but [*] undergoes
expansion, while the 2nd one doesn't.
So 1 hint to remember a variable is an internally quoted entity, such
if it is assigned to another var, it will be assigned "as-is", but
if you put double-quotes around a variable, it will replace sequences
of white space with 1 white space.
Does that address your examples' behaviors?
of some sort where '*'«»
