# start at a test suite for negative indexed array subscripts -- post bash-4.2
x=( 0 1 2 3 4 5)
declare -p x

unset 'x[-1]'
declare -p x

unset 'x[-2]'
declare -p x

unset 'x[-10]'

x[-2]=3
declare -p x

x+=( five )
declare -p x
x[-1]=5
declare -p x

x+=( [-1]=foo )
declare -p x

x[-1]=5
declare -p x

x[-2]+=four
declare -p x

echo "strlen(${x[-2]})" = ${#x[-2]}
