On Thu, Feb 24, 2011 at 02:55:13PM -0500, Steven W. Orr wrote:
> I have three arrays
>
> a1=(aaa bbb ccc ddd)
> a2=(qqq www eee rrr)
> a3=(fff ggg hhh)
>
> I then set a_all
>
> a_all=("${a1[*]}" "${a2[*]}" "${a3[*]}"
Missing ). Also, a far more serious problem, you used * when you should
have used @.
a_all=("${a1[@]}" "${a2[@]}" "${a3[@]}")
This is absolutely critical. Without this, you are no longer maintaining
the integrity of each element. In fact, what you've got there will create
a_all with precisely 3 elements. Each of these elements will be a
concatenation of the other arrays' elements with a space (or the first
char of IFS if you've set that) between them.
> Later on, I decide which element of a_all I really want. So with my new
> index calculated, I say
>
> real_a=( ${a_all[index]} )
This is also wrong. This one does word-splitting on the element you're
indexing, and the resulting set of words becomes a new array.
In fact, I can only guess what you're trying to do here.
If you want to assign a single element to a scalar variable, you
should do: element=${array[index]}
> And it worked really well until today. The problem is that I need an
> element of the aNs to be allowed to be null values.
No problem.
> Like this:
>
> a1=(aaa bbb ccc ddd '' jjj kkk lll)
No problem.
> such that if index is 0, I'd like real_a to end up with 8 elements instead
> of 7.
Huh? You mean during the concatenation? (You changed the array name?)
Do it correctly:
imadev:~$ unset a1 a2 big; a1=(a b '' c) a2=(d e f '')
imadev:~$ big=("${a1[@]}" "${a2[@]}")
imadev:~$ printf "<%s> " "${big[@]}"; echo
<a> <b> <> <c> <d> <e> <f> <>
> I could create a sentinel, I could use a case statement, I could create all
> kinds of confabulations, but I'd like to know if there's a better way to do
> it.
Huh?
> I literally tried everything I could think of.
You must learn the difference between "$*" and "$@". (And the analogous
treatment of * and @ in an array indexing context.)
imadev:~$ wrong=("${a1[*]}" "${a2[*]}")
imadev:~$ printf "<%s> " "${wrong[@]}"; echo
<a b c> <d e f >
If you don't use the right syntax, you're going to have problems with
elements that contain whitespace (or IFS characters) as well as empty
elements as you already noted.
