How to initialize an array in one step using Ruby?

You can use an array literal:

array = [ '1', '2', '3' ]

You can also use a range:

array = ('1'..'3').to_a  # parentheses are required
# or
array = *('1'..'3')      # parentheses not required, but included for clarity

For arrays of whitespace-delimited strings, you can use Percent String syntax:

array = %w[ 1 2 3 ]

You can also pass a block to Array.new to determine what the value for each entry will be:

array = Array.new(3) { |i| (i+1).to_s }

Finally, although it doesn't produce the same array of three strings as the other answers above, note also that you can use enumerators in Ruby 1.8.7+ to create arrays; for example:

array = 1.step(17,3).to_a
#=> [1, 4, 7, 10, 13, 16]

Along with the above answers , you can do this too

    =>  [*'1'.."5"]   #remember *
    => ["1", "2", "3", "4", "5"]

To prove There's More Than One Six Ways To Do It:

plus_1 = 1.method(:+)
Array.new(3, &plus_1) # => [1, 2, 3]

If 1.method(:+) wasn't possible, you could also do

plus_1 = Proc.new {|n| n + 1}
Array.new(3, &plus_1) # => [1, 2, 3]

Sure, it's overkill in this scenario, but if plus_1 was a really long expression, you might want to put it on a separate line from the array creation.

Oneliner:

array = [] << 1 << 2 << 3   #this is for fixnums.

or

 a = %w| 1 2 3 4 5 |

or

 a = [*'1'..'3']

or

 a = Array.new(3, '1')

or

 a = Array[*'1'..'3']