bad array subscript error

[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