bash array syntax

arr=()		# Create an empty array
arr=(1 2 3)	# Initialize array
${arr[2]}	# Retrieve third element
${arr[@]}	# Retrieve all elements
${!arr[@]}	# Retrieve array indices
${#arr[@]}	# Calculate array size
arr[0]=3	# Overwrite 1st element
arr+=(4)	# Append value(s)
str=$(ls)	# Save ls output as a string
arr=( $(ls) )	# Save ls output as an array of files
${arr[@]:s:n}	# Retrieve n elements starting at index s