Some single quotes...
1. `let` is more consistent with them:
$ unset A; a=" ";declare -A A; let "A['$a']++"; declare -p A
declare -A A=([" "]="1" )
$ unset A; a=" ";declare -A A; let "A[''$a]++"; declare -p A
declare -A A=([" "]="1" )
$ unset A; a=" ";declare -A A; let "A[$a'']++"; declare -p A
declare -A A=([" "]="1" )
2.
For the record.
2018-01-25 15:51 GMT+01:00 Greg Wooledge <wool...@eeg.ccf.org>:
> On Thu, Jan 25, 2018 at 02:48:47PM +0100, Tomasz Warniełło wrote:
> > Repeat-By:
> > 1.
> > $ unset A; a=" ";declare -A A; ((A[$a]++)); declare -p A
> > declare -A A
> >
> > 2.
> > $ unset A; a=" ";declare -A A; let "A[$a]=1"; declare -p A
> > declare -A A
> >
> > 3.
> > $ unset A; a=" ";declare -A A; A[$a]=1; declare -p A
> > declare -A A=([" "]="1" )
>
> The first two are using a math context. If you want the $a to survive
> intact in this context, to make it to the array, you need some single
> quotes.
>
> wooledg:~$ unset A; a=" ";declare -A A; (('A[$a]++')); declare -p A
> declare -A A=([" "]="1" )
>
> wooledg:~$ unset A; a=" ";declare -A A; let 'A[$a]=1'; declare -p A
> declare -A A=([" "]="1" )
>
> Otherwise, the parser gets all confused. I'll let someone else attempt
> a more technical explanation.
>
> The third example was not using a math context; it was just a simple
> assignment statement. That gets parsed entirely differently.
>
