Bash append a list to end element of array - arrays

Question

I am attempting to add a list to the end of a bash array that already contains elements, the array contains {a..z} and I want to add {0..9} to the end of that list, I've attempted += and this doesn't work it clears the array in my case.
while [ ! $# -eq 0 ] # Argument selector for CLI input
do
case "$1" in
--num | -n)
chars=( {0..9} )
;;
--char | -c)
chars=( {a..z} )
;;
--upper-char | -C)
chars=( {A..Z} )
;;
--help | -h)
echo "Type the program name with an argument -n for numbers -c for lowercase char and -C for uppercase"
exit
;;
esac
case "$2" in
--num | -n)
chars[${#chars[#]}]=( {0..9} )
;;
--char | -c
chars[${#chars[#]}]=( {a..z} )
;;
--upper-char | -C)
chars[${#chars[#]}]=( {A..Z} )
;;
esac
shift
done
I'm hoping to do a third case statement once I've worked out how to append lists, best case scenario is not having to hard code the array every time I want to add items.

Answer 1

Appending to an array does work with +=.
To you it appeared to be overwriting because of some other mistake in the code. This should work:
while [ ! $# -eq 0 ] # Argument selector for CLI input
do
case "$1" in
--num | -n)
chars=( {0..9} )
;;
--char | -c)
chars=( {a..z} )
;;
--upper-char | -C)
chars=( {A..Z} )
;;
--help | -h)
echo "Type the program name with an argument -n for numbers -c for lowercase char and -C for uppercase"
exit
;;
esac
case "$2" in
--num | -n)
chars+=( {0..9} )
;;
--char | -c)
chars+=( {a..z} )
;;
--upper-char | -C)
chars+=( {A..Z} )
;;
esac
shift 2
done
When it didn't work for you,
I suspect you had just shift instead of shift 2,
and expected that script.sh -c -n would give you a..z and 0..9,
but it only gave 0..9.
What happened is after just one shift,
one argument still remained to process in the while loop,
and so in the next iteration chars got replaced with a chars=(...) statement.
I propose this alternative implementation:
chars=()
while [ $# != 0 ]; do
case "$1" in
--num | -n)
chars+=( {0..9} )
;;
--char | -c)
chars+=( {a..z} )
;;
--upper-char | -C)
chars+=( {A..Z} )
;;
--help | -h)
echo "Type the program name with an argument -n for numbers -c for lowercase char and -C for uppercase"
exit 1
;;
esac
shift
done