The [] syntax in Ion is utilized to denote that the contents within should be parsed as an array expression. Array variables are also created using the same let keyword, but let makes the distinction between a string and an array by additionally requiring that all array arguments are wrapped within the [] syntax. If an array is supplied to let that is not explicitly declared as an array, then it will be coerced into a space-separated string. This design decision was made due to the possibility of an expanded array with one element being interpreted as a string.

Once created, you may call an array variable in the same manner as a string variable, but you must use the @ sigil instead of $. When expanded, arrays will be expanded into multiple arguments, so it is possible to use arrays to set multiple arguments in commands. Do note, however, that if an array is double quoted, it will be coerced into a string, which is a behavior that is equivalent to invoking the $join(array) method.

NOTE: Brace expansions also create arrays.

Arguments enclosed within brackets are treated as elements within an array.

let array = [ one two 'three four' ]

Values can be fetched from an array via their position in the array as the index.

let array = [ 1 2 3 4 5 6 7 8 9 10 ]
echo @array[0]
echo @array[5..=8]

Passing an array within brackets enables performing a deep copy of that array.

let array_copy = [ @array ]

This will join each element of the array into a string, adding spaces between each element.

let array = [ hello world ]
let as_string = @array

The ++= and ::= operators can be used to efficient concatenate an array in-place.

let array = [1 2 3]
let array ++= [5 6 7]
let array ::= 0

Arrays are useful to pass as arguments to a command. Each element will be expanded as an individual argument, if any arguments exist.

let args = [-l -a --color]
ls @args

The drop -a command will drop array variables from the shell.

let array = [one two three]
echo @array
drop -a array
echo @array