# this shows the expansions an array subscript undergoes before being run
# through the arithmetic evaluator

b=(0 1 2 3)

# array subscripts undergo variable expansion
a=2
echo ${b[$a]}

# array subscripts undergo command substitution
echo ${b[$(echo 2)]}

c='1+1'
d='1-+1'

# array subscripts are expanded and the expanded value is treated as an
# expression
echo ${b[$c]}
echo ${b[c]}

echo ${b[$d]}
echo ${b[d]}

# array subscripts undergo parameter expansion
set -- 1 2 3
echo ${b[$1]}

# array subscripts undergo tilde expansion
HOME=2
echo ${b[~]}

# array subscripts undergo word splitting -- bug in bash versions through 4.3

x='b[$d]'
IFS=-
echo $((x))
IFS=$' \t\n'

set -- 1 + 2

x='d'
IFS=-
echo $((x))
IFS=$' \t\n'

# start of quoting tests; make sure that subscript is treated as double
# quoted (inhibits word splitting) but that double quotes are silently
# discarded through quote removal

echo $(( $@ ))
echo "$(( $@ ))"

echo $(( "$x" ))
echo $(( "x" ))

unset a foo bar
a=(zero one two three four five six seven eight nine ten)

echo ${a[0]}
echo ${a["0"]}

foo=1
echo ${a[$foo]}
echo ${a["$foo"]}
echo ${a[foo]}
echo ${a["foo"]}

bar=2
echo ${a[" $bar "]}
echo ${a[" bar "]}

# tilde expansion is performed by array subscript expansion but not by posix
# style arithmetic expansion

HOME=2
echo $(( ~ ))