Re: Space as a key in an associative array - different behaviours

[Greg Wooledge]

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.