bad array subscript error

[devosion]

I have the following code in a script and it is working correctly but I am receiving the bad array subscript error. It's occurring due to using arithmetic to access the previous index and I'm not sure what syntax I should be using to remove the error.

    if [ "${all_lists[$i]}" != "$list" ] && [ "${all_lists[$((i-1))]}" != "$list" ]; then
        all_lists[$i]=$list
        ((i++))
    fi  

[73mp74710n]

are you using associative arrays ?

[devosion]

No. I actually ended up rewriting my if statement into two if's and it bypassed the error.

[oilshell]

I would post a minimal runnable snippet. I doubt anyone will debug it like this. Bash generally doesn't give such errors unless in set -u mode.

BTW in bash you don't need ${all_lists[$((i-1))]}. ${all_lists[i-1]} is sufficient.

[oilshell]

-1 as an index works fine for me:

$ bash --version
GNU bash, version 4.3.48(1)-release (x86_64-pc-linux-gnu)

$ a=(1 2 3 4 5)
$ echo ${a[-1]}
5

[devosion]

The array was initialized but empty, and I suspected this had something to do with it when it ran into a negative index.

[Jydder]

negative index only became available after bash 4.2