On Wed, Jul 09, 2025 at 11:36:59 -0400, Chet Ramey wrote:
> The arithmetic expression within (( and )) is equivalent to
>
> let "expression"
>
> so the contents are expanded once as if in double quotes. This has
> always been the case -- earlier versions of bash just translated
> ((expr)) into let "expr" internally, and the documentation was explicit
> about the equivalence.
If that's true, then I don't understand why these two commands give
different results:
(( hash[\$key]++ ))
let "hash[\$key]++"
hobbit:~$ echo "$BASH_VERSION"
5.3.0(1)-release
hobbit:~$ unset hash
hobbit:~$ declare -A hash; key=\'\]
hobbit:~$ (( hash[\$key]++ )); declare -p hash
declare -A hash=(["\$key"]="1" )
hobbit:~$ let "hash[\$key]++"; declare -p hash
declare -A hash=(["\$key"]="1" ["']"]="1" )
This example has come up a few times in the past. The behavior changed
in bash 5.2, and it looks like 5.3 is the same as 5.2 here.
This is the bash 4.0 through 5.1 result:
hobbit:~$ bash-5.1
hobbit:~$ declare -A hash; key=\'\]
hobbit:~$ (( hash[\$key]++ )); declare -p hash
declare -A hash=(["']"]="1" )
hobbit:~$ let "hash[\$key]++"; declare -p hash
declare -A hash=(["']"]="2" )
